Honeycomb body and particulate filter comprising a honeycomb

ABSTRACT

A particulate filter having a porous ceramic honeycomb structure with a first end, a second end, and a plurality of walls having wall surfaces defining a plurality of inner channels. Filtration material deposits are disposed on one or more of the wall surfaces of the honeycomb body. The highly porous deposits provide durable high clean filtration efficiency with small impact on pressure drop through the filter.

This application is a Continuation of U.S. application Ser. No.16/760,248 filed on Oct. 31, 2018 which is a national stage applicationunder 35 U.S.C § 371 of International Application No. PCT/US2018/058525,filed Oct. 31, 2018, which claims the benefit of priority to U.S.Provisional Application Ser. Nos. 62/579,601 filed on Oct. 31, 2017 and62/725,978 filed on Aug. 31, 2018, the contents of which are relied uponand incorporated herein by reference in their entireties.

BACKGROUND Field

The present specification relates honeycomb bodies, particulate filterscomprising honeycomb bodies, and methods for making such honeycombbodies and particulate filters.

Technical Background

Ceramic wall flow filters are employed to remove particulates from fluidexhaust streams, such as from combustion engine exhaust. Examplesinclude ceramic soot filters used to remove particulates from dieselengine exhaust gases; and gasoline particulate filters (GPF) used toremove particulates from gasoline engine exhaust gases. For wall flowfilters, exhaust gas to be filtered enters inlet cells and passesthrough the cell walls to exit the filter via outlet channels, with theparticulates being trapped on or within the inlet cell walls as the gastraverses and then exits the filter. The particulates may be comprisedof soot and/or ash. Accumulations of ash and/or soot typically can occurinside the filter after extended exposure to engine exhaust gases.

SUMMARY

Aspects of the disclosure pertain to ceramic articles such as honeycombbodies and particulate filters and methods for their manufacture anduse. In some embodiments, the particulate filters comprise honeycombbodies comprised of a porous ceramic honeycomb structure of porous wallscomprising wall surfaces comprising filtration material deposits, thesurfaces defining a plurality of inner channels (channels). The porouswalls are comprised of porous base walls and filtration materialdeposits disposed on one or more of the base walls, wherein the porouswalls form the channels. The filtration material deposits are comprisedof one or more inorganic materials, such as one or more ceramic orrefractory materials. The filtration material deposits are disposed onthe walls to provide enhanced filtration efficiency by the honeycombbody. In some embodiments, filtration efficiency is enhanced at least inthe use of the honeycomb body from a clean state, or from a regeneratedstate, for example when the honeycomb body has no, or substantially no,accumulation of ash or soot present inside the honeycomb body, such aswhen the honeycomb body is new or has undergone regeneration to removeall or substantially all ash and/or soot. Substantial accumulations ofash and/or soot typically can then occur inside the channels of thehoneycomb body after extended exposure to engine exhaust gases, e.g.after extended use of the honeycomb body as a filter. In one or moreembodiments, the filtration material deposits are durable, for example,possessing a durability such as resistance to a high gas or air flowthrough the particulate filter with little to no degradation in thefiltration performance.

In one or more embodiments, the filtration material deposits are presentsubstantially or even entirely at the surface of one or more of thewalls of the honeycomb structure. Thus, in some embodiments, the outersurface of the walls, which face and therefore define the channels,comprise the deposits. In some embodiments, some portions of thesurfaces of some of the walls are free of the deposits; thus some of thewalls may comprise deposit-free surface portions. In some embodiments, aportion of the filtration material deposits are disposed within theporous base wall portion, for example in the form of fingers or rootsthat extend partially into the base wall portions. In some embodimentsthe filtration material deposits are also present in the pores of theporous base wall, but do not penetrate the entire thickness of the basewall; thus, at least some interior portion of the base wall is devoid ofany deposits. In some embodiments the deposits are present as anintegrated membrane or layer at the surface of the walls, and in someembodiments an integrated continuous layer, such that at least some ofthe surfaces of the walls of the honeycomb structure are comprised ofthe membrane or layer; in some of these embodiments, the deposits arepresent across all of the surfaces of all of the walls defining one ormore of the channels, for example those base walls are completely orsubstantially completely covered by the filtration material deposits; inothers of these embodiments, the filtration material deposits arepresent on only a portion of the surfaces of the base walls of the wallsdefining one or more of the channels. The layer or membrane is porous,preferably highly porous, to allow gas flow through the layer, and thebase wall is also porous, such that gas may flow through the porouswall. In some embodiments, the layer or membrane is present as acontinuous coating over at least part of the, or over the entire,surface of the one or more walls. In some preferred embodiments, only afraction of the cell walls of the honeycomb body of the particulatefilter are provided with filtration material deposits, such as onlycells corresponding to inlet flow channels of a plugged honeycomb body.

In one aspect, the filtration material deposits are comprised offlame-deposited filtration material. In some embodiments, the porouswalls of the honeycomb structure comprise deposits present as anintegrated layer or membrane which constitute at least a portion of thesurface of the walls of one or more channels, and in some of theseembodiments at least part of, or the entire, surface of one or morewalls is comprised of the continuous layer.

In some embodiments, the surface of one or more of the walls of thehoneycomb structure are comprised of a plurality of discrete regions offiltration material deposits

In some embodiments, the filtration material deposits partially block aportion of some of the pores of the porous base walls, while stillallowing gas flow through the wall.

In one set of embodiments disclosed herein, the honeycomb body comprisesa honeycomb structure comprising a first end, a second end, and aplurality of walls extending from the first end to the second end. Theplurality of walls comprises a plurality of porous walls. The porouswalls comprise porous base walls. Surfaces of at least some of theporous walls further comprise filtration material deposits. Theplurality of walls defines a plurality of channels extending from thefirst end to the second end. Some of the channels are plugged at or nearthe first end, while some of the remaining channels are plugged at ornear the second end, thereby providing a wall-flow filter flow path thatconstitutes gas flowing from the first end into an inlet channel througha portion of the porous walls, and out through an outlet channel and outthe second end. In some embodiments, the filtration material depositsare present on walls defining one or more of the inlet channel; in someof these embodiments, the filtration material deposits are not presenton walls defining the outlet channels.

In some embodiments, the filtration material deposits are present in theform of a thin highly porous layer. In some embodiments, the porouswalls comprise an porous inorganic layer having a porosity greater than90%, and an average thickness of greater than or equal to 0.5 μm andless than or equal to 10 μm.

In another aspect, a method of making a honeycomb body, comprises:depositing filtration material onto the base walls of a ceramichoneycomb body by flowing the filtration material with gaseous carrierfluid to the ceramic honeycomb body; and binding the filtration materialto the porous base walls of the ceramic honeycomb body. In specificembodiments, the filtration material deposits are bound by thermalsintering or fusing to the base wall portion or previously laid downfiltration material. For example, deposits form a porous inorganic layerhaving a porosity of greater than 90%, and an average thickness ofgreater than or equal to 0.5 μm to less than or equal to 10 μm.

Additional features and advantages will be set forth in the detaileddescription, which follows, and in part will be readily apparent tothose skilled in the art from that description or recognized bypracticing the embodiments described herein, comprising the detaileddescription, which follows, the claims, as well as the appendeddrawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a honeycomb body according to embodimentsdisclosed and described herein;

FIG. 2 schematically depicts a honeycomb body with soot loadingaccording to embodiments disclosed and described herein;

FIGS. 3A, 3B, 3C, and 3D are scanning electron microscope (SEM) imagesof amorphous phase decomposed vaporized layer precursors deposited on ahoneycomb body according to embodiments disclosed and described herein;

FIGS. 4A, 4B, 4C, and 4D are transmission electron microscopy (TEM)images of amorphous phase decomposed vaporized layer precursorsdeposited on a honeycomb body at varying layer precursor flow ratesaccording to embodiments disclosed and described herein;

FIGS. 5A, 5B, 5C, and 5D are scanning electron microscope (SEM) imagesof crystalline phase coatings deposited on a honeycomb body according toembodiments disclosed and described herein;

FIG. 6 is a graphical depiction of filtration efficiency of a honeycombbody according to embodiments disclosed and described herein;

FIG. 7A is a graphical depiction of backpressure versus flow rate of ahoneycomb body according to embodiments disclosed and described herein;

FIG. 7B is a graphical depiction of backpressure versus soot load of ahoneycomb body according to embodiments disclosed and described herein;

FIGS. 8A and 8B are SEM photographs of a honeycomb body according toembodiments disclosed and described herein;

FIG. 9 is a graphical depiction of filtration efficiency of a honeycombbody according to embodiments disclosed and described herein;

FIG. 10A is a graphical depiction of backpressure versus flow rate of ahoneycomb body according to embodiments disclosed and described herein;

FIG. 10B is a graphical depiction of backpressure versus soot load of ahoneycomb body according to embodiments disclosed and described herein;

FIGS. 11A and 11B are SEM photographs of a honeycomb body according toembodiments disclosed and described herein;

FIG. 12 is an XRD analysis of an amorphous phase decomposed layerprecursor (as-deposited prior to sintering) and of a crystalline phaseceramic layer (after sintering);

FIGS. 13A and 13B are scanning electron microscope images at differingmagnifications of an amorphous phase decomposed layer precursordeposited on a honeycomb body according to embodiments disclosed anddescribed herein;

FIGS. 13C and 13D are scanning electron microscope images at differingmagnifications of a crystalline phase ceramic layer deposited on ahoneycomb body according to embodiments disclosed and described herein;

FIG. 14 shows an XRD scan of the decomposed layer precursor:as-deposited, after exposure to 850° C. for 6 hours, after exposure to850° C. for 12 hours, and after sintering at 1150° C. for 0.5 hours;

FIG. 15 is a graphical depiction of filtration efficiency of a honeycombbody according to embodiments disclosed and described herein;

FIG. 16A is a graphical depiction of backpressure versus flow rate of ahoneycomb body according to embodiments disclosed and described herein;

FIG. 16B is a graphical depiction of backpressure versus soot load of ahoneycomb body according to embodiments disclosed and described herein;

FIG. 17 schematically depicts a particulate filter according toembodiments disclosed and described herein;

FIG. 18 is a cross-sectional view of the particulate filter shown inFIG. 17;

FIG. 19 is a flow chart of a flame pyrolysis process according to anembodiment;

FIG. 20 is a schematic showing an experimental setup for testingparticulate filters according to one or more embodiments;

FIG. 21 is a graph of filtration efficiency vs. time (seconds) for twoexamples made in accordance with embodiments of the disclosure comparedwith a comparative example;

FIG. 22 is a graph of filtration efficiency vs. soot loading (g/L) fortwo examples made in accordance with embodiments of the disclosurecompared with a comparative example;

FIG. 23 is a graph of pressure drop vs. volume flow (m³/h) for twoexamples made in accordance with embodiments of the disclosure comparedwith a comparative example;

FIG. 24 is a graph of laboratory filtration efficiency/filtration area(%/m²) vs. laboratory pressure drop in kPA; and

FIG. 25 is a graph showing parameter NPV versus parameter NMFV forsamples prepared according to embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of honeycomb bodiescomprising a porous honeycomb body with a high porosity layer thereon,embodiments of which are illustrated in the accompanying drawings.Whenever possible, the same reference numerals will be used throughoutthe drawings to refer to the same or like parts. In embodiments, ahoneycomb body comprises a porous ceramic honeycomb body comprising afirst end, a second end, and a plurality of walls having wall surfacesdefining a plurality of inner channels. A porous inorganic layer isdisposed on one or more of the wall surfaces of the honeycomb body. Theinorganic layer has a porosity greater than 90%, and the inorganic layerhas an average thickness of greater than or equal to 0.5 μm and lessthan or equal to 10 μm. Various embodiments of honeycomb bodies andmethods of making such honeycomb bodies will be described herein withspecific reference to the appended drawings. In some embodiments, aparticulate filter is provided, the particulate filter comprising ahoneycomb body comprising a plugged porous ceramic honeycomb structurecomprising a plurality of intersecting porous walls comprising porouswall surfaces that define a plurality of channels extending from aninlet end to an outlet end of the structure, the plurality of channelscomprising inlet channels sealed at or near the outlet end and having asurface area, and outlet channels sealed at or near the inlet end andhaving a surface area, the inlet channels and the outlet channelsdefining filtration area, wherein one or more of the porous wallsurfaces defining the inlet channels comprise a base wall portion andfiltration material deposits disposed on the base wall portion, whereinthe filtration material deposits are disposed on the base wall portions,and wherein the particulate filter exhibits a change in filtrationefficiency of less than 5% after being exposed to a high flow conditionof 850 Nm³/h of air for one minute at room temperature, and wherein thechange in filtration efficiency is determined by measuring a differencebetween a number of soot particles that are introduced into theparticulate filter and a number of soot particles that exit theparticulate filter before and after exposure to the high flow condition,wherein the soot particles have a median particle size of 300 nm a sootparticle concentration of 500,000 particles/cm³ in a stream of airflowed through the particulate filter at a flow rate of 51 Nm³/h, atroom temperature, and at a velocity of 1.7 m/s as measured by a particlecounter (for example, by using a Lighthouse Handheld 3016 0.1 CFMparticle counter, available from Lighthouse Worldwide Solutions, for 30seconds upstream from the particulate filter and 30 seconds downstreamfrom the particulate filter). In some embodiments, the particulatefilter exhibits a change in filtration efficiency of less than 20%, 15%,10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or even less than 1% after exposureto the high flow condition of 850 Nm³/h of air for one minute at roomtemperature.

In some embodiments, the filtration material deposits are preferablymechanically stable, such as being resistant to dislodgement orrearrangement such as due to high gas flow through the plugged honeycombstructure of the particulate filter, and/or such as due to mechanicalvibration. In one or more embodiments, the filtration material depositsare stable when exposed to water such that the deposits maintain theirlocation or position on the cell walls. In other words, according tosome embodiments, the filtration material deposits are bound to theporous ceramic base walls. In some embodiments, the deposits arechemically bound, not just bound by physical bonding. For example, insome embodiments, the flame pyrolysis filtration material deposits arefused or sintered to the porous ceramic base wall. In addition, in someembodiments, the flame pyrolysis filtration material deposits are fusedor sintered to each other to form a layer of porous inorganic material.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

As used herein, “have”, “having”, “include”, “including”, “comprise”,“comprising” or the like are used in their open ended sense, andgenerally mean “including, but not limited to”.

A honeycomb body, as referred to herein, is a shaped ceramic honeycombstructure of intersecting walls to form cells the define channels. Theceramic honeycomb structure may be formed, extruded, or molded, and maybe of any shape or size. For example, a ceramic honeycomb structure maybe formed from cordierite or other suitable ceramic material.

A honeycomb body, as referred to herein, may also be defined as a shapedceramic honeycomb structure having at least one layer applied to wallsurfaces of the honeycomb structure, configured to filter particulatematter from a gas stream. There may be more than one layer applied tothe same location of the honeycomb structure. The layer may be inorganicor organic or both. For example, a honeycomb body may, in one or moreembodiments, be formed from cordierite or other ceramic material andhave a high porosity layer applied to surfaces of the cordieritehoneycomb structure. The layer may be “filtration material” which is toprovide enhanced filtration efficiency, both locally through and at thewall and globally through the honeycomb body. Filtration material is notconsidered to be catalytically active in that it does not react withcomponents of a gaseous mixture of an exhaust stream.

As used herein, “green” or “green ceramic” are used interchangeably andrefer to an unsintered material, unless otherwise specified.

A honeycomb body of one or more embodiments may comprise a honeycombstructure and a layer disposed on one or more walls of the honeycombstructure. In some embodiments, the layer is applied to surfaces ofwalls present within honeycomb structure, where the walls have surfacesthat define a plurality of inner channels. The inner channels, whenpresent, may have various cross-sectional shapes, such as circles,ovals, triangles, squares, pentagons, hexagons, or tessellatedcombinations or any of these, for example, and may be arranged in anysuitable geometric configuration. The inner channels, when present, maybe discrete or intersecting and may extend through the honeycomb bodyfrom a first end thereof to a second end thereof, which is opposite thefirst end.

With reference now to FIG. 1, a honeycomb body 100 according to one ormore embodiments shown and described herein is depicted. The honeycombbody 100 may, in embodiments, comprise a plurality of walls 115 defininga plurality of inner channels 110. The plurality of inner channels 110and intersecting channel walls 115 extend between first end 105 andsecond end 135 of the honeycomb body.

In one or more embodiments, the honeycomb body may be formed fromcordierite, aluminum titanate, enstatite, mullite, forsterite, corundum(SiC), spinel, sapphirine, and periclase. In general, cordierite is asolid solution having a composition according to the formula(Mg,Fe)₂Al₃(Si₅AlO₁₈). In some embodiments, the pore size of the ceramicmaterial may be controlled, the porosity of the ceramic material may becontrolled, and the pore size distribution of the ceramic material maybe controlled, for example by varying the particle sizes of the ceramicraw materials. In addition, pore formers may be included in ceramicbatches used to form the honeycomb body.

In some embodiments, walls of the honeycomb body may have an averagethickness from greater than or equal to 25 μm to less than or equal to250 μm, such as from greater than or equal to 45 μm to less than orequal to 230 μm, greater than or equal to 65 μm to less than or equal to210 μm, greater than or equal to 65 μm to less than or equal to 190 μm,or greater than or equal to 85 μm to less than or equal to 170 μm. Thewalls of the honeycomb body can be described to have a base wall portioncomprised of a bulk portion (also referred to herein as the bulk), andsurface portions (also referred to herein as the surface). The surfaceportion of the walls extends from a surface of a wall of the honeycombbody into the wall toward the bulk portion of the honeycomb body. Thesurface portion may extend from 0 (zero) to a depth of about 10 μm intothe base wall portion of the wall of the honeycomb body. In someembodiments, the surface portion may extend about 5 μm, about 7 μm, orabout 9 μm (i.e., a depth of 0 (zero)) into the base wall portion of thewall. The bulk portion of the honeycomb body constitutes the thicknessof wall minus the surface portions. Thus, the bulk portion of thehoneycomb body may be determined by the following equation:

t_(total) − 2t_(surface)where t_(total) is the total thickness of the wall and t_(surface) isthe thickness of the wall surface.

In one or more embodiments, the bulk of the honeycomb body has a bulkmean pore size from greater than or equal to 7 μm to less than or equalto 25 μm, such as from greater than or equal to 12 μm to less than orequal to 22 μm, or from greater than or equal to 12 μm to less than orequal to 18 μm. For example, in some embodiments, the bulk of thehoneycomb body may have bulk mean pore sizes of about 10 μm, about 11μm, about 12 μm, about 13 μm, about 14 μm, about 15 μm, about 16 μm,about 17 μm, about 18 μm, about 19 μm, or about 20 μm. Generally, poresizes of any given material exist in a statistical distribution. Thus,the term “median pore size” or “D₅₀” refers to which pore sizes of 50%of the pores lie and below and which the pore sizes of the remaining 50%of the pores lie, based on the statistical distribution of all thepores. Pores in ceramic bodies can be manufactured by at least one of:(1) inorganic batch material particle size and size distributions; (2)furnace/heat treatment firing time and temperature schedules; (3)furnace atmosphere (e.g., low or high oxygen and/or water content), aswell as; (4) pore formers, such as, for example, polymers and polymerparticles, starches, wood flour, hollow inorganic particles and/orgraphite/carbon particles.

In some embodiments, the bulk of the honeycomb body may have bulkporosities, not counting a coating, of from greater than or equal to 50%to less than or equal to 70% as measured by mercury intrusionporosimetry. A method for measuring surface porosity includes scanningelectron microscopy (SEM), this method in particular is valuable formeasuring surface porosity and bulk porosity independent from oneanother. In one or more embodiments, the bulk porosity of the honeycombbody may be less than 70%, less than 65%, 60%, less than 58%, less than56%, less than 54%, or less than 52%, for example.

In one or more embodiments, the surface portion of the honeycomb bodyhas a surface median pore size from greater than or equal to 7 μm toless than or equal to 20 μm, such as from greater than or equal to 8 μmto less than or equal to 15 μm, or from greater than or equal to 10 μmto less than or equal to 14 μm. For example, in some embodiments, thesurface of the honeycomb body may have surface median pore sizes ofabout 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13μm, about 14 μm, or about 15 μm.

In some embodiments, the surface of the honeycomb body may have surfaceporosities, prior to application of a layer, of from greater than orequal to 35% to less than or equal to 50% as measured SEM. In one ormore embodiments, the surface porosity of the honeycomb body may be lessthan 65%, such as less than 60%, less than 55%, less than 50%, less than48%, less than 46%, less than 44%, less than 42%, less than 40%, lessthan 48%, or less than 36% for example.

Referring now to FIGS. 17 and 18, a honeycomb body in the form of aparticulate filter 300 is schematically depicted. The particulate filter300 may be used as a wall-flow filter to filter particulate matter froman exhaust gas stream 350, such as an exhaust gas stream emitted from agasoline engine, in which case the particulate filter 300 is a gasolineparticulate filter. The particulate filter 300 generally comprises ahoneycomb body having a plurality of channels 301 or cells which extendbetween an inlet end 302 and an outlet end 404, defining an overalllength L_(a). The channels 301 of the particulate filter 300 are formedby, and at least partially defined by a plurality of intersectingchannel walls 306 that extend from the inlet end 302 to the outlet end304. The particulate filter 300 may also include a skin layer 305surrounding the plurality of channels 301. This skin layer 305 may beextruded during the formation of the channel walls 306 or formed inlater processing as an after-applied skin layer, such as by applying askinning cement to the outer peripheral portion of the channels.

An axial cross section of the particulate filter 300 of FIG. 17 is shownin FIG. 18. In some embodiments, certain channels are designated asinlet channels 308 and certain other channels are designated as outletchannels 310. In some embodiments of the particulate filter 300, atleast a first set of channels may be plugged with plugs 312. Generally,the plugs 312 are arranged proximate the ends (i.e., the inlet end orthe outlet end) of the channels 301. The plugs are generally arranged ina pre-defined pattern, such as in the checkerboard pattern shown in FIG.17, with every other channel being plugged at an end. The inlet channels308 may be plugged at or near the outlet end 304, and the outletchannels 310 may be plugged at or near the inlet end 302 on channels notcorresponding to the inlet channels, as depicted in FIG. 3. Accordingly,each cell may be plugged at or near one end of the particulate filteronly.

While FIG. 17 generally depicts a checkerboard plugging pattern, itshould be understood that alternative plugging patterns may be used inthe porous ceramic honeycomb article. In the embodiments describedherein, the particulate filter 300 may be formed with a channel densityof up to about 600 channels per square inch (cpsi). For example, in someembodiments, the particulate filter 100 may have a channel density in arange from about 100 cpsi to about 600 cpsi. In some other embodiments,the particulate filter 100 may have a channel density in a range fromabout 100 cpsi to about 400 cpsi or even from about 200 cpsi to about300 cpsi.

In the embodiments described herein, the channel walls 306 of theparticulate filter 300 may have a thickness of greater than about 4 mils(101.6 microns). For example, in some embodiments, the thickness of thechannel walls 306 may be in a range from about 4 mils up to about 30mils (762 microns). In some other embodiments, the thickness of thechannel walls 306 may be in a range from about 7 mils (177.8 microns) toabout 20 mils (508 microns).

In various embodiments the honeycomb body is configured to filterparticulate matter from a gas stream. Accordingly, the median pore size,porosity, geometry and other design aspects of both the bulk and thesurface of the honeycomb body are selected taking into account thesefiltration requirements of the honeycomb body. As an example, and asshown in the embodiment of FIG. 2, a wall 210 of the honeycomb body 200has layer 220 disposed thereon, preferably sintered or otherwise bondedby heat treatment. The layer 220 may comprise particles 225 that aredeposited on the wall 210 of the honeycomb body 200 and help preventparticulate matter from exiting the honeycomb body along with the gasstream 230, such as, for example, soot and ash, and to help prevent theparticulate matter from clogging the base wall portion of the walls 210of the honeycomb body 200. In this way, and according to embodiments,the layer 220 can serve as the primary filtration component while thebase wall portion of the honeycomb body can be configured to otherwiseminimize pressure drop for example as compared to conventional honeycombbodies without such layer. Pressure drop, as used herein, is measuredusing a differential pressure sensor to measure the drop in pressureacross the axial length of the filter. Because pore size of the layer220 is smaller than that of the base wall portion, the layer will filtermost of the smaller-sized particulate matter, but it is expected thatthe base wall portion of the walls of the honeycomb body filter iseffective to filter some of the larger-sized particulate matter. As willbe described in further detail herein, the honeycomb body may be formedby a suitable method—such as, for example, a flame depositionmethod—that allows for a thin, highly porous layer to be formed on atleast some surfaces of the walls of the honeycomb body.

In one or more embodiments, the porosity of the layer disposed on thewalls of the honeycomb body, as measured by SEM, is greater than orequal to 80%, such as greater than 90%. In other embodiments, theporosity of the layer disposed on the walls of the honeycomb body isgreater than or equal to 92%, such as greater than or equal to 93%, orgreater than or equal to 94%. In still other embodiments, the porosityof the layer disposed on the walls of the honeycomb body is greater thanor equal to 95%, such as greater than or equal to 96%, or greater thanor equal to 97%. In various embodiments, the porosity of the layerdisposed on the walls of the honeycomb body is less than or equal to99%, such as less than or equal to 97%, less than or equal to 95%, lessthan or equal to 94%, or less than or equal to 93%. The high porosity ofthe layer on the walls of the honeycomb body allows for the layer to beapplied to a honeycomb body without significantly affecting the pressuredrop of the honeycomb body compared to the pressure drop of an identicalhoneycomb body that does not comprise a layer thereon. SEM and X-raytomography are useful for measuring surface and bulk porosityindependently of one another. Obtaining porosity by density calculationincludes: measuring weight of the inorganic layer and its thickness toobtain a layer density and calculating porosity of the layer accordingto the equation: layer porosity=1−layer density/inorganic materialdensity. As an example, for a layer comprising mullite, the “inorganicmaterial density” is the density of mullite.

As mentioned above, the layer on walls of the honeycomb body is verythin compared to thickness of the base wall portion of the walls of thehoneycomb body, and the layer also has very high porosity andpermeability. As will be discussed in further detail below, the layer onthe honeycomb body can be formed by methods that permit the layer to beapplied to surfaces of walls of the honeycomb body in very thin layers.In embodiments, the average thickness of the layer on the base wallportion of the walls of the honeycomb body is from greater than or equalto 0.5 μm to less than or equal to 30 μm, such as from greater than orequal to 0.5 μm to less than or equal to 20 μm, greater than or equal to0.5 μm to less than or equal to 10 μm, such as from greater than orequal to 0.5 μm to less than or equal to 5 μm, from greater than orequal to 1 μm to less than or equal to 4.5 μm, from greater than orequal to 1.5 μm to less than or equal to 4 μm, or from greater than orequal to 2 μm to less than or equal to 3.5 μm.

As discussed above, the layer can be applied to the walls of thehoneycomb body by methods that permit the inorganic layer to have asmall median pore size. This small median pore size allows the layer tofilter a high percentage of particulate and prevents particulate frompenetrating honeycomb and settling into the pores of the honeycomb, asdescribed above with reference to FIG. 2. The small median pore size oflayer according to embodiments increases the filtration efficiency ofthe honeycomb body. In one or more embodiments, the layer on the wallsof the honeycomb body has a median pore size from greater than or equalto 0.1 μm to less than or equal to 5 μm, such as from greater than orequal to 0.5 μm to less than or equal to 4 μm, or from greater than orequal to 0.6 μm to less than or equal to 3 μm. For example, in someembodiments, the layer on the walls of the honeycomb body may havemedian pore sizes of about 0.5 μm, about 0.6 μm, about 0.7 μm, about 0.8μm, about 0.9 μm, about 1 μm, about 2 μm, about 3 μm, or about 4 μm.

Although the layer on the walls of the honeycomb body may, inembodiments, cover substantially 100% of the wall surfaces defininginner channels of the honeycomb body, in other embodiments, the layer onthe walls of the honeycomb body covers less than substantially 100% ofthe wall surfaces defining inner channels of the honeycomb body. Forinstance, in one or more embodiments, the layer on the walls of thehoneycomb body covers at least 70% of the wall surfaces defining innerchannels of the honeycomb body, covers at least 75% of the wall surfacesdefining inner channels of the honeycomb body, covers at least 80% ofthe wall surfaces defining inner channels of the honeycomb body, coversat least 85% of the wall surfaces defining inner channels of thehoneycomb body, covers at least 90% of the wall surfaces defining innerchannels of the honeycomb body, or covers at least 85% of the wallsurfaces defining inner channels of the honeycomb body.

As described above with reference to FIG. 1, the honeycomb body can havea first end and second end. The first end and the second end areseparated by an axial length. In some embodiments, the layer on thewalls of the honeycomb body may extend the entire axial length of thehoneycomb body (i.e., extends along 100% of the axial length). However,in other embodiments, the layer on the walls of the honeycomb bodyextends along at least 60% of the axial length, such as extends along atleast 65% of the axial length, extends along at least 70% of the axiallength, extends along at least 75% of the axial length, extends along atleast 80% of the axial length, extends along at least 85% of the axiallength, extends along at least 90% of the axial length, or extends alongat least 95% of the axial length.

In embodiments, the layer on the walls of the honeycomb body extendsfrom the first end of the honeycomb body to the second end of thehoneycomb body. In some embodiments, the layer on the walls of thehoneycomb body extends the entire distance from the first surface of thehoneycomb body to the second surface of the honeycomb body (i.e.,extends along 100% of a distance from the first surface of the honeycombbody to the second surface of the honeycomb body). However, in one ormore embodiments, the layer on the walls of the honeycomb body extendsalong 60% of a distance between the first surface of the honeycomb bodyand the second surface of the honeycomb body, such as extends along 65%of a distance between the first surface of the honeycomb body and thesecond surface of the honeycomb body, extends along 70% of a distancebetween the first surface of the honeycomb body and the second surfaceof the honeycomb body, extends along 75% of a distance between the firstsurface of the honeycomb body and the second surface of the honeycombbody, extends along 80% of a distance between the first surface of thehoneycomb body and the second surface of the honeycomb body, extendsalong 85% of a distance between the first surface of the honeycomb bodyand the second surface of the honeycomb body, extends along 90% of adistance between the first surface of the honeycomb body and the secondsurface of the honeycomb body, or extends along 95% of a distancebetween the first surface of the honeycomb body and the second surfaceof the honeycomb body.

In one or more embodiments, the layer on the walls of the honeycomb bodyis disposed on the wall surfaces as a continuous coating. As used hereina “continuous coating” is an area where no portion of the area isessentially bare, or free of the layer material. In one or moreembodiments, at least 50% of the layer is disposed on the wall surfacesof the honeycomb body as a continuous layer, such as at least 60% of thelayer is disposed on the wall surfaces of the honeycomb body as acontinuous layer, at least 70% of the layer is disposed on the wallsurfaces of the honeycomb body as a continuous layer, at least 80% ofthe layer is disposed on the wall surfaces of the honeycomb body as acontinuous layer, at least 90% of the layer is disposed on the wallsurfaces of the honeycomb body as a continuous layer, at least 92% ofthe layer is disposed on the wall surfaces of the honeycomb body as acontinuous layer, at least 94% of the layer is disposed on the wallsurfaces of the honeycomb body as a continuous layer, at least 96% ofthe layer is disposed on the wall surfaces of the honeycomb body as acontinuous layer, or at least 98% of the layer is disposed on the wallsurfaces of the honeycomb body as a continuous layer. In otherembodiments 100% of the layer is disposed on the wall surfaces of thehoneycomb body as a continuous layer.

As stated above, and without being bound by any particular theory, it isbelieved that a low pressure drop is achieved by honeycomb bodies ofembodiments because the layer on the honeycomb body is a primaryfiltration component of the honeycomb body, which allows for moreflexibility in designing a honeycomb body. The selection of a honeycombbody having a low pressure drop in combination with the low thicknessand high porosity of the layer on the honeycomb body according toembodiments allows a honeycomb body of embodiments to have a lowpressure drop when compared to conventional honeycomb bodies. Inembodiments, the layer is in the range of from 0.1 to 30 g/L on thehoneycomb body. In embodiments, the layer may be present in the rangeof: from 0.2 to 20 g/L, from 0.3 to 25 g/L, from 0.4 to 20 g/L, from 1to 10 g/L. In some embodiments, the pressure drop (i.e., a cleanpressure drop without soot or ash) across the honeycomb body as comparedto a honeycomb without a thin high porosity inorganic layer is less thanor equal to 10%, such as less than or equal to 9%, or less than or equalto 8%. In other embodiments, the pressure drop across the honeycomb bodyis less than or equal to 7%, such as less than or equal to 6%. In stillother embodiments, the pressure drop across the honeycomb body is lessthan or equal to 5%, such as less than or equal to 4%, or less than orequal to 3%.

As stated above, and without being bound to any particular theory, smallpore sizes in the layer on the walls of the honeycomb body allow thehoneycomb body to have good filtration efficiency even before ash orsoot build-up occurs in the honeycomb body. The filtration efficiency ofhoneycomb bodies is measured herein using the protocol outlined inTandon et al., 65 Chemical engineering Science 4751-60 (2010). As usedherein, the initial filtration efficiency of a honeycomb body refers toa honeycomb body in a clean state, such as new or regenerated honeycombbody, that does not comprise any measurable soot or ash loading. Inembodiments, the initial filtration efficiency (i.e., clean filtrationefficiency) of the honeycomb body is greater than or equal to 70%, suchas greater than or equal to 80%, or greater than or equal to 85%. In yetother embodiments, the initial filtration efficiency of the honeycombbody is greater than 90%, such as greater than or equal to 93%, orgreater than or equal to 95%, or greater than or equal to 98%.

The layer on the walls of the honeycomb body according to embodiments isthin and has a high porosity, and in some embodiments the layer on wallsof the honeycomb body also has good chemical durability and physicalstability. Particularly if solidified, sintered, or otherwise bonded tothe surface of the honeycomb body after the layer material is applied tothe walls of the honeycomb body, as will be discussed in more detailbelow. The chemical durability and physical stability of the layer onthe honeycomb body can be determined, in embodiments, by subjecting thehoneycomb body to test cycles comprising burn out cycles and an agingtest and measuring the initial filtration efficiency before and afterthe test cycles. For instance, one exemplary method for measuring thechemical durability and the physical stability of the honeycomb bodycomprises measuring the initial filtration efficiency of a honeycombbody; loading soot onto the honeycomb body under simulated operatingconditions; burning out the built up soot at about 650° C.; subjectingthe honeycomb body to an aging test at 1050° C. and 10% humidity for 12hours; and measuring the filtration efficiency of the honeycomb body.Multiple soot build up and burnout cycles may be conducted. A smallchange in filtration efficiency (ΔFE) from before the test cycles toafter the test cycles indicates better chemical durability and physicalstability of the layer on the honeycomb body. In some embodiments, theΔFE is less than or equal to 5%, such as less than or equal to 4%, orless than or equal to 3%. In other embodiments, the ΔFE is less than orequal to 2%, or less than or equal to 1%.

In some embodiments, the layer on the walls of the honeycomb body may becomprised of one or a mixture of ceramic components, such as, forexample, ceramic components selected from the group consisting of SiO₂,Al₂O₃, MgO, ZrO₂, CaO, TiO₂, CeO₂, Na₂O, Pt, Pd, Ag, Cu, Fe, Ni, andmixtures thereof. Thus, the layer on the walls of the honeycomb body maycomprise an oxide ceramic or an aluminum silicate. As discussed in moredetail below, the method of making the layer on the honeycomb bodyaccording to embodiments can allow for customization of the layercomposition for a given application. This may be beneficial because theceramic components may be combined to match, for example, the physicalproperties—such as, for example coefficient of thermal expansion (CTE)and Young's modulus, etc.—of the honeycomb body, which can improve thephysical stability of the honeycomb body. In some embodiments, the layeron the walls of the honeycomb body may comprise cordierite, aluminumtitanate, enstatite, mullite, forsterite, corundum (SiC), spinel,sapphirine, and periclase. In some embodiments, the cordierite, aluminumtitanate, enstatite, mullite, forsterite, corundum (SiC), spinel,sapphirine, and/or periclase is synthetic. In one or more embodiments,the inorganic layer comprises a synthetic mullite. Mullite is a rarealuminium silicate mineral and can form two stoichiometric forms3Al₂O₃.2SiO₂ or 2Al₂O₃.SiO₂, in accordance with the general structurexAl₂O₃·ySiO₂. Preparation of synthetic mullite includes process controlsto target 1.5≤x/y≤2 or to target Al/Si mass ratio in the range of 2.9 to3.8.

In some embodiments, the composition of the layer on the walls of thehoneycomb body is the same as the composition of the honeycomb body.However, in other embodiments, the composition of the layer is differentfrom the composition of the honeycomb body.

The layer, according to one or more embodiments, has a permeability of≥10⁻¹⁵ m². In some embodiments the layer has a permeability of ≥10⁻¹⁴m², such as ≥10⁻¹³ m², or ≥10⁻¹² m².

In some embodiments, the layer is comprised of mullite and has anaverage particle size from greater than or equal to 5 nm to less than orequal to 3 μm. In such embodiments, the thickness and porosity of thelayer may be a thickness depending on the desired properties of thehoneycomb body.

In some embodiments, the layer is comprised of alumina and has anaverage particle size from greater than or equal to 10 nm to less thanor equal to 3 μm. In some embodiments the average particle size is fromgreater than or equal to 100 nm to less than or equal to 3 μm, such asgreater than or equal to 500 nm to less than or equal to 3 μm, orgreater than or equal to 500 nm to less than or equal to 2 μm. In suchembodiments, the thickness and porosity of the layer on the honeycombbody may be a thickness depending on the desired properties of thehoneycomb body.

The properties of the layer and, in turn, the honeycomb body overall areattributable to the ability of applying a thin, high porosity layerhaving small median pore sizes to a honeycomb body.

Methods of making a honeycomb body according to some embodimentsdisclosed and described herein comprise: atomizing, vaporizing, ormisting a layer precursor so that the layer precursor may be carried bya gaseous carrier fluid; depositing the atomized, vaporized, or mistedlayer precursor on a ceramic honeycomb structure; and binding theatomized, vaporized, or misted layer precursor to the ceramic honeycombstructure to form a layer on the ceramic honeycomb structure. Inembodiments, the gaseous carrier fluid can be, for example, air, oxygen,or nitrogen. In some embodiments, the layer precursor may be combinedwith a solvent—such as a solvent selected from the group consisting ofmethoxyethanol, ethanol, water and mixtures thereof—before the layerprecursor is atomized, vaporized, or misted. The layer precursor is, inone or more embodiments, blown into inner channels of the ceramichoneycomb structure. The layer precursor particles may be bound to theceramic honeycomb structure by a suitable method including applyingmoisture—such as, for example, steam or humidity—heat, or radiation—suchas, for example, microwaves—to the layer precursor after the layerprecursor has been deposited on the ceramic honeycomb structure.

Methods of making a honeycomb body according to some embodimentsdisclosed and described herein comprise flame pyrolysis deposition of alayer to a ceramic honeycomb structure, which provides for deposition ofa very thin layer having a high porosity and small median pore size. Inembodiments, methods of making a honeycomb body comprise: vaporizing alayer precursor to form a vaporized layer precursor by contacting thelayer precursor with a vaporizing gas (the layer precursor may comprisea precursor material and a solvent); decomposing the vaporized layerprecursor by contacting the vaporized layer precursor with a flame;depositing the vaporized layer precursor on a ceramic honeycombstructure; and sintering the vaporized layer precursor to form thehoneycomb body, wherein the honeycomb body comprises a layer that coatsat least a portion of walls of the ceramic honeycomb structure. In oneor more embodiments, the layer precursor is selected from the groupconsisting of CaO, Ca(OH)₂, CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃,Al(OH)₃, calcium aluminates, magnesium aluminates, and mixtures thereof.

In some embodiments, the method of forming a honeycomb body comprisesforming or obtaining a layer precursor that comprises a ceramicprecursor material and a solvent. The ceramic precursor material of thelayer precursor comprises conventional raw ceramic materials that serveas a source of, for example, SiO₂, Al₂O₃, TiO₂, MgO, ZrO₂, CaO, CeO₂,Na₂O, Pt, Pd, Ag, Cu, Fe, Ni, and the like. For example, in someembodiments, the ceramic precursor material is selected from the groupconsisting of tetraethyl orthosilicate, magnesium ethoxide andaluminum(III) tri-sec-butoxide, trimethylaluminum, AlCl₃, SiCl₄,Al(NO₃)₃, aluminum isopropoxide, octamethyl cyclotetrasiloxane, andmixtures thereof. The solvent used in the layer precursor is notparticularly limited as long as it is capable of maintaining asuspension of the ceramic precursor material within the solvent, and thesolvent is capable of being vaporized at temperatures less than 200° C.In embodiments, the solvent is selected from the group consisting ofmethoxyethanol, ethanol, water, xylene, methanol, ethylacetate, benzene,and mixtures thereof.

In some embodiments, the layer precursor is vaporized to form avaporized layer precursor by contacting the layer precursor with avaporizing fluid. In one or more embodiments, the vaporizing fluid isselected from the group consisting of oxygen (O₂), water (steam, H₂O),nitrogen (N₂), and mixtures thereof. The vaporizing fluid is flowed at ahigh flow rate relative to the flow rate of the layer precursor so thatwhen the vaporizing fluid contacts the layer precursor, the layerprecursor is vaporized to a molecular level by the vaporizing fluid. Forexample, in embodiments, the vaporizing fluid is a gas that is flowed ata flow rate from greater than or equal to 3 L/min to less than or equalto 100 L/min mL/min, such as from greater than or equal to 4 L/min toless than or equal to 6.5 L/min, or from greater than or equal to 25L/min to less than or equal to 35 L/min. In other embodiments, thevaporizing gas is flowed at a flow rate from greater than or equal to 60L/min to less than or equal to 70 L/min.

The flow rate of the gaseous vaporizing fluid is, in embodiments,greater than the flow rate of the layer precursor. Accordingly, in oneor more embodiments, the layer precursor is flowed at a flow rate fromgreater than or equal to 1.0 mL/min to less than or equal to 50 mL/min,such as from greater than or equal to 3 mL/min to less than or equal to5 mL/min, or from greater than or equal to 25 mL/min to less than orequal to 35 mL/min. The flow rate of the vaporizing fluid and the flowrate of the layer precursor can be controlled so that the layerprecursor is vaporized when it is contacted with the vaporizing fluid.

According to some embodiments, once the layer precursor has beencontacted with the vaporizing fluid to form the vaporized layerprecursor, the vaporized layer precursor is decomposed by contacting thevaporized layer precursor with a flame. The flame may be formed bycombusting a suitable combustion gas, such as, for example, oxygen,methane, ethane, propane, butane, natural gas, or mixtures thereof. Oncethe vaporized layer precursor contacts the flame, the energy from theflame causes the vaporized layer precursor to decompose to atomic-levelcomponents, and the solvent is combusted into gases, such as, forexample, hydrogen (H₂), carbon dioxide (CO₂), and carbon monoxide (CO).This combustion provides elemental components of the ceramic precursormaterials well dispersed in a gas. In one or more embodiments, the flametemperature is from greater than or equal to 800 K to less than or equalto 2500 K. This allows the vaporized layer precursor to be easilydirected to and deposited on a honeycomb body. It should be understoodthat in embodiments one flame may be used to decompose the layerprecursor; however, in other embodiments two or more flames may be usedto decompose the layer precursor. In yet other embodiments, thevaporized layer precursor is not decomposed by a flame.

In one or more embodiments, the vaporized layer precursor, which iswell-dispersed in a fluid, is directed to a honeycomb body, such as byusing a wind tunnel or differential pressure to guide the vaporizedlayer precursor to the honeycomb body. Thereby, the vaporized layerprecursor is deposited on the honeycomb body. In some embodiments, thehoneycomb body may have one or more of the channels plugged on one end,such as, for example, the first end 105 of the honeycomb body during thedeposition of the vaporized layer precursor to the honeycomb body. Theplugged channels may, in some embodiments, be removed after depositionof the layer precursor. But, in other embodiments, the channels mayremain plugged even after deposition of the layer precursor. The patternof plugging channels of the honeycomb body is not limited, and in someembodiments all the channels of the honeycomb body may be plugged at oneend. In other embodiments, only a portion of the channels of thehoneycomb body may be plugged at one end. In such embodiments, thepattern of plugged and unplugged channels at one end of the honeycombbody is not limited and may be, for example, a checkerboard patternwhere alternating channels of one end of the honeycomb body are plugged.By plugging all or a portion of the channels at one end of the honeycombbody during deposition of the vaporized layer precursor, the vaporizedlayer precursor may be evenly distributed within the channels 110 of thehoneycomb body 100.

The vaporized layer precursor is, in some embodiments, deposited on thehoneycomb body as an amorphous phase. For example, as discussed above,the ceramic precursor materials can be broken down to an elemental levelin the decomposed layer precursor. The elemental components can be mixedtogether at an elemental level when deposited to the honeycomb body. Forexample, FIG. 3A is a scanning electron microscope (SEM) image of anamorphous phase of 5SiO₂·2Al₂O₃·2MgO decomposed layer precursordeposited on the surface of a honeycomb body; FIG. 3B is an SEM image ofan amorphous phase of 2SiO₂·3Al₂O₃ decomposed layer precursor depositedon the surface of a honeycomb body; FIG. 3C is an SEM image of anamorphous phase of 2SiO₂·5Al₂O₃·4MgO decomposed layer precursordeposited on the surface of honeycomb body; and FIG. 3D is an SEM imageof an amorphous phase of Al₂O₃·MgO decomposed layer precursor depositedon the surface of a honeycomb body. As can be seen in each of FIGS.3A-3D, particles at an elemental level are dispersed in an amorphousphase upon the honeycomb body. In this amorphous phase, the decomposedlayer precursor, which has been deposited on the honeycomb body, has aporosity, as calculated, for example, according to the density of thelayer versus the density of the inorganic material of the layer—ofgreater than or equal to 95%, such as greater than or equal to 96%, orgreater than or equal to 97%. In other embodiments, the amorphous phasedecomposed layer precursor has a porosity of greater than or equal to98%, or greater than or equal to 99%.

The porosity and pore size of the amorphous vaporized layer precursorand ultimately, the layer on the honeycomb body may, in someembodiments, be modified by the mean particle size of vaporized layer.The mean particle size of the vaporized layer may be controlled by theflow rate of layer precursor. For instance, as shown in FIGS. 4A-4D, themean particle size of the vaporized layer precursor increases as theflow rate of the layer precursor increases. FIG. 4A a transmissionelectron microscopy (TEM) image of an amorphous 5SiO₂·2Al₂O₃·2MgOdecomposed layer precursor deposited at layer precursor a flow rate of 3mL/min; FIG. 4B is a TEM image of an amorphous 5SiO₂·2Al₂O₃·2MgOdecomposed layer precursor deposited at a layer precursor flow rate of 1mL/min; FIG. 4C is a TEM image of an amorphous 2SiO₂·3Al₂O₃ decomposedlayer precursor deposited at a layer precursor flow rate of 1 mL/min;and FIG. 4D is a TEM image of an amorphous 5SiO₂·2Al₂O₃·2MgO decomposedlayer precursor and an amorphous 2SiO₂·3Al₂O₃ decomposed layer precursordeposited using a dual flame processes with both flames having a layerprecursor flow rate of 1 mL/min. As shown in FIGS. 4A-4D, the elementsof the decomposed layer precursor were mixed at atomic level, forming ahomogeneous phase having varying particle sizes depending on the flowrate of the layer precursor. However, in embodiments, the mean particlesize of the vaporized layer precursor is from greater than or equal to 5nm to less than or equal to 3 μm, such as from greater than or equal to100 nm to less than or equal to 3 μm, or from greater than or equal to200 nm to less than or equal to 1 μm. In other embodiments, the meanparticle size of the vaporized layer precursor is from greater than orequal to 15 nm to less than or equal to 500 nm, such as from greaterthan or equal to 20 nm to less than or equal to 200 nm, or from greaterthan or equal to 25 nm to less than or equal to 100 nm.

As noted above, the chemical durability and physical stability can beimparted to the layer on the walls of the honeycomb body according tosome embodiments disclosed and described herein. To improve theseproperties, the vaporized layer precursor can be, in one or moreembodiments, sintered or otherwise bonded to the honeycomb body after ithas been deposited on the honeycomb body to form a layer as acrystalline phase that coats at least a portion of the honeycomb body.According to embodiments, sintering the vaporized layer precursorcomprises heating the vaporized layer precursor after it has beendeposited on the honeycomb body to temperatures from greater than orequal to 950° C. to less than or equal to 1150° C., such as from greaterthan or equal to 1000° C. to less than or equal to 1100° C., fromgreater than or equal to 1025° C. to less than or equal to 1075° C., orabout 1050° C. The duration of the sintering is, in some embodiments,from greater than or equal to 20 minutes to less than or equal to 2.0hours, such as from greater than or equal to 30 minutes to less than orequal to 1.5 hours, or from greater than or equal to 45 minutes to lessthan or equal to 1.0 hour. After sintering the vaporized layer precursorto form the honeycomb body, the layer is a crystalline phase. Forinstance, FIG. 5A is an SEM image of a sintered, crystalline phase5SiO₂·2Al₂O₃·2MgO ceramic layer deposited on a honeycomb body; FIG. 5Bis an SEM image of a sintered, crystalline phase 2SiO₂·3Al₂O₃ ceramiclayer deposited on a honeycomb body; FIG. 5C is an SEM image of asintered, crystalline phase 2SiO₂·5Al₂O₃·4MgO ceramic layer deposited ona honeycomb body; and FIG. 5D is an SEM image of a sintered, crystallinephase Al₂O₃.MgO ceramic layer deposited on a honeycomb body. Accordingto embodiments, the sintered, crystalline phase layers have a porosity,measured by SEM, of greater than 90%, such as greater than or equal to91%, or greater than or equal to 92%. In other embodiments, thesintered, crystalline phase layer has a porosity of greater than orequal to 93%, such as greater than or equal to 94%, or greater than orequal to 95%. In still other embodiments, the sintered, crystallinephase layer has a porosity of greater than or equal to 96%, such asgreater than or equal to 97%, or greater than or equal to 98%.

According to one or more embodiments of the disclosure, particulatefilters are characterized by the filtration efficiency, representingtheir ability to remove a certain fraction of particulates from anincoming gas stream. The particulates can be characterized by their massconcentrations or their number concentrations. Both values typicallycorrelate closely. Using a generic concentration C_(Particulate) withthe units particulate mass or number per unit volume, the filtrationefficiency FE is typically obtained from the equation:

$\begin{matrix}{{FE} = \frac{\lbrack C_{Particulate} \rbrack_{Inlet} - \lbrack C_{Particulate} \rbrack_{outlet}}{\lbrack C_{Particulate} \rbrack_{Inlet}}} & {{Eqn}.\;(1)}\end{matrix}$

There are different means for the experimental measurement of thefiltration efficiency. A schematic for a generic laboratory setup isshown in FIG. 20. The generic laboratory setup comprises a gas supply,e.g. air, adjusted to a define flow rate, a particulate generator, forexample one that generates soot particles at a certain rate andconcentration, a filter sample to be tested, and two particulateanalyzers at the inlet and the outlet of the filter samples.

The experiment is performed at controlled temperature, for example, roomtemperature. As used herein, “room temperature” refers to a temperatureof 20° C. During the experiment, the gas flow is adjusted to a constantflow rate. Then particulates are added to the gas. Across the filtersample, a certain portion of the particulates are removed by filtration,which is measured as difference between the inlet and the outletparticle concentration. An example of such an experiment is shown inFIG. 21, for two experimental samples A and B made in accordance withthe embodiments described herein plotted against a conventional sample(Comparative). In the example shown, the particles were soot particlesgenerated on a soot generator and the volumetric flow rate was 21 m³/h.The testing was conducted at room temperature and atmospheric pressure.Plotted is the filtration efficiency calculated from the inlet andoutlet concentration according to eqn. (1) vs. the time of theexperiment. At time t=0 s the dosing of the particles starts and thefiltration efficiency is recorded. For the different filter samples,different values in filtration efficiency are observed.

As shown in FIG. 21, the filtration efficiency in all cases increaseswith time. The reason for this is that the accumulated particlesthemselves, soot in this case, act as a filtration medium, enhancing theoverall efficiency. To illustrate this more effectively it is helpful toplot the filtration as function of the accumulated soot mass instead ofthe time. The soot mass is obtained as the difference between the sootentering the filter and the soot mass leaving the filter integrated overtime. The data from FIG. 21 in this format are provided in FIG. 22.

The filtration efficiency at the beginning, time equal t=0 s or 0 g/Lsoot load is usually called “clean” or “fresh” filtration efficiency andis determined only by the characteristics of the filter sample. Based onfiltration theory the filtration process occurs based on differentmechanism, primarily depending on the size of the particles. A commonmodel to describe filtration media is the concept of an assembly of unitcollectors. For the soot generated by the soot generator of theexperiments described above, the dominating filtration mechanism is thatbased on Brownian motion of the small soot particles. The collectionefficiency of a unit collector based on the Brownian motion mechanismη_(BM) can be described by:

$\begin{matrix}{\eta_{BM} = {4 \cdot \frac{A_{s}^{1/3}}{{Pe}_{i}^{2/3}} \cdot ( {1 - ɛ} )^{2/3}}} & {{Eqn}.\;(2)}\end{matrix}$

A_(s) is a parameter, primarily dependent on the porosity ε and Pe_(i)being the Peclet number. The Peclet number is proportional to the fluidvelocity inside the pore space u_(w)/ε and the ratio between collectordiameter d_(c) and diffusion coefficient for Brownian motion D_(BM).

$\begin{matrix}{{Pe_{i}} = {\frac{u_{w}}{ɛ} \cdot \frac{d_{c}}{D_{{BM},i}}}} & {{Eqn}.\;(3)}\end{matrix}$

The particle size d_(s) and temperature T dependence of this collectionmechanism are introduced via the Brownian diffusion coefficient,D_(BM)˜(T/ds²). Combining all parameters that depend on themicrostructure of the filtration medium into a single variableK_(microstructure), eqn.(2) can be rewritten as Eqn. (4):

$\begin{matrix}{\eta_{BM} = {K_{Microstructure} \cdot ( \frac{D_{BM}}{u_{w}} )^{2/3}}} & {{Eqn}.\;(4)}\end{matrix}$

The fluid velocity uw is determined from the volumetric flow ratedivided by the cross-sectional area or filtration area. Thus, inaddition to microstructural characteristics, the filtration performanceat a given flow rate and particle size is proportional to the filtrationarea of a filter. Therefore, to compare materials with differentmicrostructures, the filtration efficiency is normalized by thefiltration area. For honeycomb wall flow filters with alternatelyplugged channels, the filtration surface area FSA in m² can be obtainedfrom eqn. (5):

$\begin{matrix}{{FSA} = {\frac{GSA}{2} \cdot V_{Filter}}} & {{Eqn}.\;(5)}\end{matrix}$

In eqn. (5) GSA is the geometric surface area per volume of filter andV_(Filter) is the volume of the filter sample. The factor ½ originatesfrom the fact that only one half of the channels represent inletchannels through which the gas enters and then flows across the porousfilter wall. Filtration area (or total filtration) would be total inletcells area+total outlet cells area=total area. In other words, in eqn.(5), the total inlet cells area, which can be calculated by total areadivided by 2 if the total inlet cells area=total outlet cells area.However, if the total inlet cells area is not equal to the total outletcells area, the denominator in the equation would have to be modified toreflect this.

In addition to the filtration performance filters, are commonlycharacterized by their resistance to flow, usually referenced aspressure drop across the sample at a given volumetric gas flow rate.Often higher filtration performance coincides with an increased pressuredrop or resistance to flow. From an application point of view, it isusually desirable to have an as low as possible pressure drop, as thepressure drop usually means pumping losses. In motor vehicleapplications, this results in a reduction in power available to propelthe vehicle or a reduction in fuel efficiency.

The pressure drop behavior of a filter sample is usually assessed bymeasuring the difference in pressure up and downstream of the filtersample at a given volumetric flow rate. In laboratory measurements thiscan be done at room temperature and at different flow rates. In FIG. 24,an example of pressure drop measurements is shown. Plotted is thepressure difference across the filter sample at different volumetricflow rates several experimental examples prepared according to theExamples described in this disclosure plotted against commerciallyavailable wall flow honeycomb particulate filters, both bare andcontaining catalytic coating. The testing was performed at roomtemperature. As a characteristic value, the pressure drop determined inthese tests was used at the highest flow rate explored, 357 m³/h atnormal conditions.

The filtration efficiency as well as the pressure drop performance asdescribed above were tested over a wide range of filter samplesavailable from prior art as well as for a number of inventive sampleswith a composite microstructure. For filtration the initial or cleanfiltration efficiency in % is considered (flow rate of 21 m³/h) andnormalized by the filtration surface area of each sample. The pressuredrop was assessed at the highest flow rate of 357 m³/h.

In FIG. 24, the data obtained from commercially available wall flowhoneycomb particulate filters (Comparative) and samples made accordingto the Examples described herein are summarized. The commerciallyavailable wall flow honeycomb particulate filters (Comparative)comprised a number of uncoated filter samples with differentmicrostructure and composition as well as filters that have been coatedwith different catalytic washcoats. As shown in FIG. 24, the Examplesprepared according the instant disclosure are located in a differentregion of the filtration-pressure drop performance space of the graph,namely above the dotted line shown in FIG. 24. The dotted line,described by equation (6) can be defined as:(Filtration Efficiency/Filtration area)≥A+B×(Clean Pressure Drop)   Eqn.(6):

The filtration efficiency represents the clean or initial filtrationefficiency in % at 21 m³/h and room temperature, the filtration area inm² and the clean pressure drop being measured at room temperature at 357m³/h. The constants A and B are defined as follows:

A=35%/m²; B=9%/(m² kPa).

According to one or more embodiments, the particulate filters preparedaccording to the embodiments described herein exhibit advantageouslyhigh filtration efficiencies normalized to filtration area of the inletchannels. Thus, according to one or more embodiments, the particulatefilters described herein provide high filtration efficiency in a fresh(new) state, immediately after installation in vehicles in the factoriesof car manufacturers. In some embodiments, this high filtrationefficiency is provided with a low pressure drop.

While the claims of the present disclosure are not to be limited by aparticular theory, it is believed that the pressure drop of aparticulate filters is composed of five primary factors. These factorsinclude contraction and expansion of the gas flow at the inlet andoutlet of the filter, friction losses of the gas flow along the inletand outlet channel, and pressure drop of the gas flow across the porouschannel walls.

In general, pressure drop across a filter is affected by macroscopicgeometric parameters such as part diameter, length, hydraulic diameterof the channels and open frontal area as well as by the permeability ofthe porous filter wall. The latter is the only material characteristicand is defined by the microstructure, for example, the porosity, theeffective pore size and the pore connectivity. Since the gas flowthrough the pores is laminar, the frictional losses across the wall aredetermined by the entire path across the porous wall.

The inlet and outlet contributions of the pressure drop can be describedby

$\begin{matrix}{{\Delta\; p_{({1,5})}} = {( {\zeta_{in} + \zeta_{out}} ) \cdot \rho_{g} \cdot \ ( \frac{Q \cdot L}{V_{Filler} \cdot {OFA}} )^{2}}} & {{Eqn}.\;(7)}\end{matrix}$

With Δp as pressure drop, ρ_(g) as density of the gas, Q as volume flowrate, V_(Filter) as filter volume, L as length of the filter, OFA asopen frontal area of the filter and ζ_(in) and ζ_(out) as empiricalcontraction and expansion coefficients, respectively.

For the pressure drop inside the filter the equation provided as eqn.(26) in SAE Technical Paper 2003-01-0842 can be used, presented as Eqn.(8) herein.

$\begin{matrix}{{\Delta p_{({2,3,4})}} = {\frac{Q_{eff}}{2} \cdot \frac{\mu}{V_{Filter}} \cdot ( {d_{h} + t_{w}} )^{2} \cdot ( {\frac{t_{w}}{d_{h} \cdot \kappa_{effective}} + \frac{8 \cdot F \cdot L^{2}}{3 \cdot d_{h}^{4}}} )}} & {{Eqn}.\;(8)}\end{matrix}$

With the new variables μ as dynamic viscosity, Q_(eff) as effectivevolume flow rate, d_(h) as hydraulic channel diameter, t_(w) as wallthickness, F as friction factor (F=28.45 for square channels) andκ_(effective) as effective permeability of the wall. The effectivevolume flow rate differs from the total flow rate by a factor thatconsiders the flow rate distribution along the inlet and outlet channel.It was found empirically that Q_(eff)=1.32*Q provides for a betterdescription of experimental results.

The total pressure drop as measured in an experiment would be the sum ofthe contributions described by equation (7) and equation (8). Inequation (7) and (8), all parameters are known and can be easilydetermined with the exception of the effective permeability of the wallmaterial.

The effective permeability κ_(effective) can be extracted fromexperimental data using equations (7) and (8). For this purpose, thepressure drop contribution due to inlet contraction and outletexpansion, eqn. (7), is subtracted from the experimental pressure dropvalue, providing for Eqn. (9)Δp _((2,3,4)) =Δp _(Experimental) −Δp _((1,5))   Eqn. (9):

Combining Eqn.(9) with Eqn.(8) and solving for the effective wallpermeability κ_(effective) yields:

$\begin{matrix}{\kappa_{{effectiv}e} = {\frac{t_{w}}{d_{h}} \cdot \lbrack {\frac{{\Delta p_{Experi{mental}}} - {\Delta p_{({1,5})}}}{\frac{\mu \cdot Q_{eff}}{2 \cdot V_{Filter}} \cdot ( {d_{h} + t_{w}} )^{2}} - \frac{8 \cdot F \cdot L^{2}}{3 \cdot d_{h}^{4}}} \rbrack^{- 1}}} & {{Eqn}.\mspace{11mu}(10)}\end{matrix}$

The permeability of the porous wall of an extruded honeycomb body, κ₀,can usually be described reasonably well by the product of porosity εand the square of the effective median pore size D₅₀, both determined bymercury porosimetry, divided by 66.7:

$\begin{matrix}{\kappa_{0} = \frac{ɛ \cdot D_{50}^{2}}{6{6.7}}} & {{Eqn}.\mspace{11mu}(11)}\end{matrix}$

If coatings or other modifications are applied to the “as extruded” basewall portions of the porous wall with permeability κ₀ the permeabilitychanges to a new effective permeability value, κ_(effective), which canfor example be determined using Eqn.(10) from experimental pressure dropvalues. This change in permeability relative to the permeability of theas extruded base wall portions of the honeycomb wall can also bedescribed by a “Normalized Permeability Value (NPV),” describing theratio of the effective permeability to the permeability of thenon-modified original microstructure:NPV=κ_(effective)/(εD ₅₀ ²/66.7)_(bare)   Eqn.(12)

The experimental pressure drop measurement to determineΔp_(experimental) of a filter sample can be assessed by measuring thedifference in pressure up and downstream of the filter sample at a givenvolumetric flow rate. In laboratory measurements this can be done atroom temperature and at different flow rates. In FIG. 23, an example ofpressure drop measurements is shown. Plotted is the pressure differenceacross the filter sample at different volumetric flow rates. The testingwas performed at room temperature. As a characteristic value, thepressure drop determined in these tests at the highest flow rateexplored, 357 m³/h at normal conditions was used.

As discussed above, particulate filters are characterized by thefiltration efficiency, representing their ability to remove a certainfraction of particulates from an incoming gas stream. The particulatescan be characterized by their mass concentrations or their numberconcentrations. Both values typically correlate closely. Using a genericconcentration C_(Particulate) with the units particulate mass or numberper unit volume, the filtration efficiency FE is typically obtained fromEqn.(1) above.

Using the schematic for the generic laboratory setup is shown in FIG.20, a particulate filter is tested at room temperature, a constant flowrate and then adding particulates are added to the gas. Across thefilter sample, a certain portion of the particulates are removed byfiltration, which is measured as difference between the inlet and theoutlet particle concentration. An example of such an experiment is shownin FIG. 21, for two experimental samples A and B made in accordance withthe embodiments described herein plotted against a conventional sample(Comparative). In the example shown, the particles were soot particlesgenerated on a soot generator and the volumetric flow rate was 21 m³/hat normal conditions. The testing was done at room temperature. Plottedis the filtration efficiency calculated from the inlet and outletconcentration according to eqn. (1) vs. the time of the experiment. Attime t=0 s the dosing of the particles starts and the filtrationefficiency is recorded. For the different filter samples, differentvalues in filtration efficiency are observed.

As shown in FIG. 21, the filtration efficiency in all cases increaseswith time. The reason for this is that the accumulated particlesthemselves, soot in this case, act as a filtration medium, enhancing theoverall efficiency. To illustrate this more effectively it is helpful toplot the filtration as function of the accumulated soot mass instead ofthe time. The soot mass is obtained as the difference between the sootentering the filter and the soot mass leaving the filter integrated overtime. The data from FIG. 21 in this format are provided in FIG. 22.

The filtration efficiency, as discussed above, at the beginning, timeequal t=0 s or 0 g/L soot load is usually called “clean” or “fresh”filtration efficiency and is determined only by the characteristics ofthe filter sample. Based on filtration theory the filtration processoccurs based on different mechanism, primarily depending on the size ofthe particles. A common model to describe filtration media is theconcept of an assembly of unit collectors. For the soot generated by thesoot generator of the experiments described above, the dominatingfiltration mechanism is that based on Brownian motion of the small sootparticles. The collection efficiency of a unit collector based on theBrownian motion mechanism η_(BM) can be described by Eqn. (2). Asdiscussed above, the Peclet number is proportional to the fluid velocityinside the pore space u_(w)/ε and the ratio between collector diameterd_(c) and diffusion coefficient for Brownian motion D_(BM) as shown byEqn. (3) above.

SAE Technical Paper 2012-01-0363 explains that for an uncoated extrudedfilter with “random” porous microstructure, the clean filtrationefficiency can be correlated to a filtration characteristic parameterA_(Filt), which is proportional to microstructural as well asmacroscopic filter properties, Eqn. (13):

$\begin{matrix}{{A_{Filt}\text{∼}{\frac{ɛ^{{0.4}3}}{D_{50}^{5/3}} \cdot \frac{t_{w} \cdot ({CPSI})}{( {Q\text{/}V_{Filter}} )^{2/3}}}} = {{EMF} \cdot \frac{t_{w} \cdot ({CPSI})}{( {Q\text{/}V_{Filter}} )^{2/3}}}} & {{Eqn}.\mspace{11mu}(13)}\end{matrix}$

As new variables, Eqn. (13) has CPSI as cell density of the filterstructure. A correlation between the clean filtration efficiency andthis filtration characteristic parameter (A_(FILT)) can be plotted on agraph with clean filtration efficiency on the Y axis and the filtrationcharacteristic parameter (A_(FILT)) on the X axis.

The contribution from the microstructural parameters, porosity andmedian pore size can be combined to an Effective Microstructure Factor,EMF. For materials for which the effective porosity and median pore sizeare not known, this new parameter can be used to characterize theeffective properties of the microstructure. This variable also allowsconsideration of in real microstructures, that the filtration does notnecessarily occur along the entire length of the pore across the filterwall, but rather to a larger extent locally at locations where favorableconditions exist for the collection and deposition of particles, e.g.passages with a narrow opening (“pore neck”). As soon as some particlesare collected they further narrow this pore neck, accelerating thefiltration process further. Thus, the new parameter allows forconsideration of microstructures which are non-homogeneous and do nothave a random pore design.

Analogous to what has been done for pressure drop, it is also useful toconsider not only the new microstructure parameter EMF, but alsonormalize it for the properties of the base microstructure of the basewall portions of the as extruded filter body with random microstructure.For the latter the EMF is obtained as ratio of porosity ε^(0.43) dividedby the median pore size D₅₀ to the power of 5/3. Through thisnormalization we obtain the new Normalized Microstructure FiltrationValue, NMFV, to describe the filtration characteristics of amicrostructure as: Eqn.(14): NMFV=EMF/(ε^(0.43)/D₅₀^(5/3))_(base wall properties)

According to one or more embodiments, particulate filters are providedthat yield a favorable (e.g. high) Normalized Permeability Value (NPV)while, at the same time, provide for an increase in the NormalizedMicrostructure Filtration Value (NMFV), e.g. materials that provide forlow (change) in pressure drop combined with increased clean filtration.

The filtration efficiency as well as the pressure drop performance asdescribed above were tested over a wide range of filter samplesavailable from prior art as well as for a number of samples made inaccordance with the present disclosure with a composite microstructureof porous wall surfaces defining the inlet channels, namely, inletchannels are comprised of the filtration material deposits as describedaccording to one or more embodiments herein. For filtration, the initialor clean filtration efficiency in % is considered at a flow rate of 21m³/h. The pressure drop was assessed at room temperature and the highestflow rate of 357 m³/h.

The performance characteristics of the reference examples (e.g.,commercially existing filters) and examples prepared in accordance withembodiments of the instant disclosure can be plotted. The NormalizedMicrostructure Filtration Value (NMFV) can be plotted on the Y axisversus clean filtration on the X axis to examine the data. A more usefulplot of Normalized Permeability Value (NPV) on the Y axis versus theNormalized Microstructure Filtration Value (NMFV) on the X axis is shownin FIG. 25 for commercially available gasoline particulate filters andparticulate filters prepared according to the Examples of the presentdisclosure (black diamonds). FIG. 25 shows that the particulate filterexamples prepared according to the present disclosure exhibit both (1)an NPV value that is greater than 0.2 and (2) an NMFV value that isgreater than 2. None of the commercially available gasoline particulatefilters that were tested met both of these criteria. The domain of theNormalized Microstructure Filtration ValueNMFV=EMF/(ε^(0.43)/D^(5/3))_(base wall properties) of 2 or larger and aNormalized Permeability Value NPV=κ_(effective)/(εD₅₀²/66.7)_(base wall properties) of 0.2 or larger is clearly novel andunique to the inventive particulate filters. Particulate filters thatoccupy this domain in which both (1) the NPV value is greater than 0.2and (2) the NMFV value is greater than 2 exhibit advantageously highfiltration efficiencies. Thus, according to one or more embodiments, theparticulate filters described herein provide high filtration efficiencyin a fresh (new) state, immediately after installation in vehicles inthe factories of car manufacturers. In some embodiments, this highfiltration efficiency is provided with a low pressure drop.

Honeycomb bodies and methods of making honeycomb bodies have beendescribed herein. In embodiments, the honeycomb bodies comprise a layeronto at least one surface of a honeycomb body. The layer, inembodiments, has a crystalline structure, high porosity, such as greaterthan 90%, and the layer is applied as a thin layer, such as having athickness of greater than or equal to 0.5 μm to less than or equal to 10μm. It should be understood that in various of the embodiments describedabove a “honeycomb body” may be a ceramic “honeycomb body” and a “layer”may be a ceramic “layer.”

Numbered embodiments as disclosed and described herein are now provided.

1. A honeycomb body comprising:

-   -   a porous ceramic honeycomb structure comprising a first end, a        second end, and a plurality of walls having wall surfaces        defining a plurality of inner channels; and    -   a porous inorganic layer disposed on one or more of the wall        surfaces, wherein    -   the porous inorganic layer has a porosity greater than 90%, and    -   the porous inorganic layer has an average thickness of greater        than or equal to 0.5 μm and less than or equal to 30 μm.

2. The honeycomb body of embodiment 1, wherein the porous inorganiclayer has an average thickness of less than or equal to 20 μm.

3. The honeycomb body of embodiment 1 or 2, wherein the porous inorganiclayer has an average thickness of less than or equal to 10 μm.

4. The honeycomb body of any of embodiments 1-3, wherein the porousinorganic layer comprises an oxide ceramic or an aluminum silicate.

5. The honeycomb body of any of embodiments 1-4, wherein the porousinorganic layer covers at least 70% of the wall surfaces.

6. The honeycomb body of any of embodiments 1-5, wherein the porousinorganic layer covers at least 90% of the wall surfaces.

7. The honeycomb body of embodiment 1, wherein the first end and thesecond end are spaced apart by an axial length, and the porous inorganiclayer extends at least 60% along the axial length.

8. The honeycomb body of any of embodiments 1-7, wherein the porousinorganic layer extends at least 60% of a distance between the first endand the second end.

9. The honeycomb body of any of embodiments 1-8, wherein greater than90% of the porous inorganic layer is disposed on the wall surfaces as acontinuous coating.

10. The honeycomb body of any of embodiments 1-9, wherein the porousceramic honeycomb structure has a porosity greater than or equal to 50%.

11. The honeycomb body of any of embodiments 1-10, wherein the porousceramic honeycomb structure has a porosity greater than or equal to 55%.

12. The honeycomb body of any of embodiments 1-11, wherein the porousceramic honeycomb structure has a porosity from greater than or equal to50% to less than or equal to 70%.

13. The honeycomb body of any of embodiments 1-12, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 10 μm.

14. The honeycomb body of any of embodiments 1-13, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 15 μm.

15. The honeycomb body of any of embodiments 1-14, wherein the porousceramic honeycomb structure has a bulk median pore size from greaterthan or equal to 8 μm to less than or equal to 25 μm.

16. The honeycomb body of any of embodiments 1-15, wherein the porousceramic honeycomb structure has a porosity greater than or equal to 35%.

17. The honeycomb body of any of embodiments 1-16, wherein the porousceramic honeycomb structure has a porosity greater than or equal to 40%.

18. The honeycomb body of any of embodiments 1-15, wherein the porousceramic honeycomb structure has a porosity from greater than or equal to35% to less than or equal to 60%.

19. The honeycomb body of any of embodiments 1-18, wherein the porousceramic honeycomb structure has a surface median pore size greater thanor equal to 8 μm.

20. The honeycomb body of any of embodiments 1-19, wherein the porousceramic honeycomb structure has a surface median pore size greater thanor equal to 10 μm.

21. The honeycomb body of any of embodiments 1-19, wherein the porousceramic honeycomb structure has a surface median pore size from greaterthan or equal to 8 μm to less than or equal to 20 μm.

22. The honeycomb body of any of embodiments 1-21, wherein the porosityof the porous inorganic layer is greater than 95%.

23. The honeycomb body of any of embodiments 1-22, wherein the porosityof the porous inorganic layer is less than or equal to 98%.

24. The honeycomb body of any of embodiments 1-23, wherein the averagethickness of the porous inorganic layer is greater than or equal to 1 μmto less than or equal to 20 μm.

25. The honeycomb body of any of embodiments 1-24, wherein the averagethickness of the porous inorganic layer is greater than or equal to 1 μmto less than or equal to 10 μm.

26. The honeycomb body of any of embodiments 1-25, wherein the porousinorganic layer has a median pore size from greater than or equal to 0.1μm to less than or equal to 5 μm.

27. The honeycomb body of any of embodiments 1-26, wherein the porousinorganic layer has a median pore size from greater than or equal to 0.1μm to less than or equal to 4 μm.

28. The honeycomb body of any of embodiments 1-27, wherein the porousinorganic layer is comprised of particles having a mean particle sizefrom greater than or equal to 5 nm to less than or equal to 3 μm.

29. The honeycomb body of any of embodiments 1-27, wherein the porousinorganic layer is comprised of particles having a mean particle sizefrom greater than or equal to 100 nm to less than or equal to 3 μm.

30. The honeycomb body of any of embodiments 1-27, wherein the porousinorganic layer is comprised of particles having a mean particle sizefrom greater than or equal to 200 nm to less than or equal to 1 μm.

31. The honeycomb body of any of embodiments 1-29, wherein the porousinorganic layer is comprised of at least one of alumina, mullite, or(Al₂O₃)_(x)(SiO₂)_(y), where x equals 2 or 3 and y equals 1 or 2 havinga mean particle size from greater than or equal to 5 nm to less than orequal to 3 μm.

32. The honeycomb body of embodiment 31, wherein the porous inorganiclayer has a mean particle size from greater than or equal to 100 nm toless than or equal to 3 μm.

33. The honeycomb body of embodiment 31, wherein the porous inorganiclayer has a mean particle size from greater than or equal to 200 nm toless than or equal to 1 μm.

34. The honeycomb body of any of embodiments 1-27, wherein the porousinorganic layer is comprised of alumina having a mean particle size fromgreater than or equal to 5 nm to less than or equal to 3 μm.

35. The honeycomb body of embodiment 34, wherein the porous inorganiclayer is comprised of alumina having a mean particle size from greaterthan or equal to 100 nm to less than or equal to 3 μm.

36. The honeycomb body of embodiment 34, wherein the porous inorganiclayer is comprised of alumina having a mean particle size from greaterthan or equal to 200 nm to less than or equal to 3 μm.

37. The honeycomb body of any of embodiments 1-30, wherein the porousinorganic layer comprises a member selected from the group consisting ofSiO₂, Al₂O₃, MgO, ZrO₂, CaO, TiO₂, CeO₂, Na₂O, Pt, Pd, Ag, Cu, Fe, Ni,and mixtures thereof.

38. The honeycomb body of embodiment 37, wherein the porous inorganiclayer has an amorphous structure.

39. The honeycomb body of embodiment 37, wherein the porous inorganiclayer has a crystalline structure.

40. The honeycomb body of any of embodiments 1-39, wherein the porousinorganic layer has a permeability is greater than or equal to 10⁻¹⁵ m².

41. The honeycomb body of any of embodiments 1-39, wherein the porousinorganic layer has a permeability is greater than or equal to 10⁻¹⁴ m².

42. The honeycomb body of any of embodiments 1-39, wherein the porousinorganic layer has a permeability is greater than or equal to 10⁻¹³ m².

43. The honeycomb body of any of embodiments 1-39, wherein the porousinorganic layer has a permeability is greater than or equal to 10⁻¹² m².

44. The honeycomb body of any of embodiments 1-43, wherein the porousinorganic layer is free from cracks having a width greater than 5 μm andlength greater than 1 mm.

45. The honeycomb body of any of embodiments 1-44, wherein at least aportion of the inner channels are plugged at the first end of the porousceramic honeycomb body.

46. The honeycomb body of any of embodiments 1-45, wherein at least aportion of the inner channels are plugged at the second end of theporous ceramic honeycomb body.

47. The honeycomb body of embodiments 1-46, wherein the honeycomb bodyhas an initial filtration efficiency of greater than or equal to 75%measured with 120 nm particulate at 21 Nm³/h.

48. The honeycomb body of embodiments 1-47, wherein the honeycomb bodyhas an initial filtration efficiency of greater than or equal to 90%.

49. The honeycomb body of embodiments 1-45, wherein a filtrationefficiency of the honeycomb body is greater than or equal to 70%measured with 120 nm particulate at a velocity of 1.7 meters/second anda soot load equal to 0.01 g/L.

50. The honeycomb body of embodiment 49, wherein the filtrationefficiency of the honeycomb body is greater than or equal to 80%.

51. The honeycomb body of embodiment 50, wherein the filtrationefficiency of the honeycomb body is greater than or equal to 90%.

52. The honeycomb body of embodiment 51, wherein the filtrationefficiency of the honeycomb body is greater than or equal to 95%measured.

53. The honeycomb body of embodiment 45, wherein a maximum pressure dropacross the honeycomb body is less than or equal to 20%.

54. The honeycomb body of embodiment 45, wherein a maximum pressure dropacross the honeycomb body is less than or equal to 10%.

55. The honeycomb body of any of embodiments 1-54, wherein the porousinorganic layer comprises synthetic mullite.

56. The honeycomb body of any of embodiments 1-55, wherein the porousinorganic layer is sintered to one or more of the wall surfaces.

57. A ceramic filter article comprising:

-   -   a porous ceramic body comprising a honeycomb structure comprised        of a plurality of walls, each of the walls comprising a porous        ceramic base wall portion, wherein there is a first group of the        walls, and wherein each of the first group of walls further        comprises a surrogate retentate layer forming an outermost wall        layer, the outermost wall layers defining a first group of        channels, wherein the surrogate retentate layer has a porosity        greater than 90% and an average thickness of greater than or        equal to 0.5 μm and less than or equal to 30 μm.

58. The ceramic filter article of embodiment 57, wherein the surrogateretentate layer is comprised of a first porous inorganic layer.

59. The ceramic filter article of embodiment 57, wherein the surrogateretentate layer is comprised of a first porous organic layer.

60. The ceramic filter article of embodiment 57, wherein the porousceramic base wall portion is comprised of a predominant base ceramicphase and the first porous inorganic layer is comprised of a predominantfirst ceramic phase which is different from the base ceramic phase.

61. The ceramic filter article of embodiment 60, wherein the baseceramic phase comprises cordierite.

62. The ceramic filter article of embodiment 60, wherein the firstceramic phase is comprised of alumina or silica, or a combinationthereof.

63. The ceramic filter article of embodiment 60, wherein the firstceramic phase is selected from the group consisting of CaO, Ca(OH)₂,CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃, Al(OH)₃, calcium aluminates,magnesium aluminates, and mixtures thereof.

64. The ceramic filter of any of embodiments 58-63, wherein the firstporous inorganic layer comprises synthetic mullite.

65. The ceramic filter of any of embodiments 58-63, wherein the firstporous inorganic layer is sintered to the porous ceramic base wallportion.

66. A ceramic filter article comprising:

-   -   a porous ceramic body comprising a honeycomb structure comprised        of a plurality of walls defining a plurality of channels, each        wall being comprised of a porous ceramic base wall portion,        wherein at least some of the walls comprise a first porous        inorganic outer layer disposed on the porous ceramic base wall        portion, the first porous inorganic outer layer providing a        first outermost wall surface, wherein the plurality of walls        intersect to define first channels surrounded by the first        outermost wall surfaces,    -   wherein the first porous inorganic layer has a porosity greater        than 90%, and an average thickness of greater than or equal to        0.5 μm and less than or equal to 30 μm.

67. The ceramic filter article of embodiment 66, wherein the wallsfurther comprise a second outermost wall surface provided by the porousceramic base wall portion, and the second outermost wall surfaces definea plurality of second channels surrounded by the second outermost wallsurfaces.

68. The ceramic filter article of embodiment 66, wherein at least amajority of the first channels are open at a first end of the porousceramic body and sealed at a second end of the porous ceramic body, andwherein at least a majority of the second channels are open at a secondend of the porous ceramic body and sealed at a first end of the porousceramic body.

69. The ceramic filter article of embodiment 66, wherein at least someof the walls comprise a second porous inorganic outer layer disposed onthe porous ceramic base wall portion, the second porous inorganic outerlayer providing a second outermost wall surface, wherein the pluralityof walls intersect to define second channels surrounded by the secondoutermost wall surfaces.

70. The ceramic filter article of embodiment 66, wherein at least amajority of the first channels are open at a first end of the porousceramic body and sealed at a second end of the porous ceramic body, andwherein at least a majority of the second channels are open at a secondend of the porous ceramic body and sealed at a first end of the porousceramic body.

71. The ceramic filter article of embodiment 66, wherein the porousceramic base wall portion has a porosity in the range between 30% and70%.

72. The ceramic filter article of embodiment 66, wherein the porousceramic base wall portion has a porosity in the range between 30% and70%.

73. The ceramic filter article of embodiment 66, wherein the firstporous inorganic outer layer is comprised of flame deposition particles.

74. The ceramic filter article of embodiment 62, wherein the firstporous inorganic outer layer is comprised of CVD particles.

75. The ceramic filter of any of embodiments 66-74, wherein the firstporous inorganic layer comprises synthetic mullite.

76. The ceramic filter of any of embodiments 66-75, wherein the firstporous inorganic layer is sintered to the porous ceramic base wallportion.

77. A ceramic filter article comprising:

a porous ceramic body comprising a honeycomb structure comprised of aplurality of walls, wherein at least some of the walls comprise opposingfirst and second surfaces and a base wall portion disposed between thefirst and second surfaces, and the plurality of walls intersect todefine first channels by the first surfaces and second channels with thesecond surfaces, wherein at least the first surfaces or the secondsurfaces are at least partially provided by a porous inorganic layerdisposed on the base wall portion, wherein the porous inorganic layerhas a porosity greater than 90%, and the porous inorganic layer has anaverage thickness of greater than or equal to 0.5 μm and less than orequal to 30 μm.

78. The ceramic filter article of embodiment 77, wherein both the firstand second surfaces are at least partially provided by a porousinorganic layer disposed on the base wall portion.

79. The ceramic filter article of embodiment 77, wherein the porousinorganic layer is disposed on the inlet surfaces of at least some ofthe walls.

80. The ceramic filter article of embodiment 77, wherein the porousinorganic layer is disposed only on the inlet surfaces of at least someof the walls.

81. The ceramic filter article of embodiment 77, wherein the outletsurfaces are free of any porous inorganic layer.

82. The ceramic filter of any of embodiments 77-81, wherein the porousinorganic layer comprises synthetic mullite.

83. The ceramic filter of any of embodiments 77-82, wherein the porousinorganic layer is sintered to the base wall portion.

84. A particulate filter comprising:

a honeycomb body comprising a plugged porous ceramic honeycomb structurecomprising a plurality of intersecting porous walls arranged in a matrixof cells, the porous walls comprising porous wall surfaces that define aplurality of channels extending from an inlet end to an outlet end ofthe structure, the plurality of channels comprising inlet channelssealed at or near the outlet end and having a surface area, and outletchannels sealed at or near the inlet end and having a surface area;

wherein one or more of the porous wall surfaces defining the inletchannels comprise a base wall portion and filtration material depositsdisposed on the base wall portion such that at least a portion of theporous wall surfaces defining the inlet channels are comprised of thefiltration material deposits forming a porous inorganic layer having aporosity greater than 90%;

wherein the honeycomb body comprises a total inlet surface area (SATOT)which is a sum of the surface areas of all the porous walls defining theinlet channels;

wherein the particulate filter induces a pressure drop (DP) for a flowof air through the particulate filter (AIRSCFM) at an air temperature(AIRTEMP), the flow of air containing particulates having an averagesize of 100 nm;

wherein, when the particulate filter contains less than 0.01 grams ofthe particulates per volume of the honeycomb structure in liters (g/L),the particulate filter traps the particulates being carried by the flowof air into the particulate filter with a filtration efficiency (FE)measured at AIRTEMP=room temperature and at a flow rate of 21 m³/h suchthat FE/SATOT is greater than (9*DP+35) in units of %/m², with DP inunits of kPa measured at a flow rate of 357 m³/h and measured atAIRTEMP=room temperature; and

wherein the base wall portion is comprised of a first ceramiccomposition, and the filtration material deposits are comprised ofsecond ceramic composition, and the first and second ceramiccompositions differ.

85. The particulate filter of embodiment 84, wherein the porousinorganic layer has average thickness of greater than or equal to 0.5 μmand less than or equal to 30 μm.

86. The particulate filter of embodiments 84 or 85, wherein the secondceramic composition is comprised of alumina or silica, or a combinationthereof.

87. The particulate filter of embodiments 84 or 85, wherein the secondceramic composition is selected from the group consisting of CaO,Ca(OH)₂, CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃, Al(OH)₃, calciumaluminates, magnesium aluminates, and mixtures thereof.

88. The particulate filter of embodiments 84 of 85, wherein the secondceramic composition is cordierite and the second ceramic composition isalumina.

89. The particulate filter of embodiments 76 or 77, wherein the porousinorganic layer comprises an oxide ceramic or an aluminum silicate.

90. The particulate filter of any of embodiments 84-89, wherein theporous inorganic layer covers at least 70% of the porous wall surfaces.

91. The particulate filter of any of embodiments 76-81, wherein theporous inorganic layer covers at least 90% of the porous wall surfaces.

92. The particulate filter of any of embodiments 84-89, wherein theinlet end and the outlet end are spaced apart by an axial length, andthe porous inorganic layer extends at least 60% along the axial length.

93. The particulate filter of any of embodiments 84-89, wherein theporous inorganic layer extends at least 60% of a distance between theinlet end and the outlet end.

94. The particulate filter of any of embodiments 84-89, wherein greaterthan 90% of the porous inorganic layer is disposed on the porous wallsurfaces as a continuous coating.

95. The particulate filter of any of embodiments 84-94, wherein theporous ceramic honeycomb structure has a porosity from greater than orequal to 50% to less than or equal to 70%.

96. The particulate filter of any of embodiments 84-95, wherein theporous ceramic honeycomb structure has a bulk median pore size greaterthan or equal to 10 μm.

97. The particulate filter of any of embodiments 84-95, wherein theporous ceramic honeycomb structure has a bulk median pore size greaterthan or equal to 15 μm.

98. The particulate filter of any of embodiments 84-95, wherein theporous ceramic honeycomb structure has a bulk median pore size fromgreater than or equal to 8 μm to less than or equal to 25 μm.

99. The particulate filter of embodiment 84, wherein the filtrationmaterial deposits comprise synthetic mullite.

100. The ceramic filter of embodiment 84, wherein the filtrationmaterial deposits are sintered to the porous ceramic base wall portion.

101. A particulate filter comprising:

a honeycomb body comprising a plugged porous ceramic honeycomb structurecomprising a plurality of intersecting porous walls comprising porouswall surfaces that define a plurality of channels extending from aninlet end to an outlet end of the structure, the plurality of channelscomprising inlet channels sealed at or near the outlet end and having asurface area, and outlet channels sealed at or near the inlet end andhaving a surface area, the inlet channels and the outlet channelsdefining filtration area;

wherein one or more of the porous wall surfaces defining the inletchannels comprise a base wall portion and filtration material depositsdisposed on the base wall portion such that at least a portion of theporous wall surfaces defining the inlet channels are comprised of thefiltration material deposits forming a porous inorganic layer having aporosity greater than 90%; and

wherein the particulate filter exhibits a clean filtration efficiency in% per filtration area in m² that is equal to or greater than a value of(A+B*Clean Pressure Drop), A and B are defined as A=35%/m² and B=9%/(m²kPa), the clean filtration efficiency measured at room temperature andat a flow rate of 21 m³/h on a particulate filter having a soot load ofless than 0.01 g/L, and the clean pressure drop measured at a flow rateof 357 m³/h on a soot free filter.

102. The particulate filter of embodiment 101, wherein one or more ofthe porous wall surfaces defining the inlet channels comprise a basewall portion comprised of a first ceramic composition and filtrationmaterial deposits disposed on the base wall portion are comprised of asecond ceramic composition, and the first and second ceramiccompositions differ.

103. The particulate filter of embodiment 101, wherein the porousinorganic layer has average thickness of greater than or equal to 0.5 μmand less than or equal to 30 μm.

104. The particulate filter of embodiment 101, wherein the secondceramic composition is comprised of alumina or silica, or a combinationthereof.

105. The particulate filter of embodiment 101, wherein the secondceramic composition is selected from the group consisting of CaO,Ca(OH)₂, CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃, Al(OH)₃, calciumaluminates, magnesium aluminates, and mixtures thereof.

106. The particulate filter of embodiment 101, wherein the first ceramiccomposition is cordierite and the second ceramic composition is alumina.

107. The particulate filter of embodiment 101, wherein the porousinorganic layer comprises an oxide ceramic or an aluminum silicate.

108. The particulate filter of embodiment 101, wherein the porousinorganic layer covers at least 70% of the porous wall surfaces.

109. The particulate filter of embodiment 101, wherein the porousinorganic layer covers at least 90% of the porous wall surfaces.

110. The particulate filter of embodiment 101, wherein the inlet end andthe outlet end are spaced apart by an axial length, and the porousinorganic layer extends at least 60% along the axial length.

111. The particulate filter of embodiment 106, wherein the porousinorganic layer extends at least 60% of a distance between the inlet endand the outlet end.

112. The particulate filter of embodiment 101, wherein greater than 90%of the porous inorganic layer is disposed on the porous wall surfaces asa continuous coating.

113. The particulate filter of embodiment 101, wherein the porousceramic honeycomb structure has a porosity from greater than or equal to50% to less than or equal to 70%.

114. The particulate filter of embodiment 106, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 10 μm.

115. The particulate filter of embodiment 101, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 15 μm.

116. The particulate filter of embodiment 101, wherein the porousceramic honeycomb structure has a bulk median pore size from greaterthan or equal to 8 μm to less than or equal to 25 μm.

117. The particulate filter of embodiment 101, wherein the filtrationmaterial deposits comprise synthetic mullite.

118. The ceramic filter of embodiment 84, wherein the filtrationmaterial deposits are sintered to the porous ceramic base wall portion.

119. A particulate filter comprising:

a honeycomb body comprising a plugged porous ceramic honeycomb structurecomprising a plurality of intersecting porous walls comprising porouswall surfaces that define a plurality of channels extending from aninlet end to an outlet end of the porous ceramic honeycomb structure,the plurality of channels comprising inlet channels sealed at or nearthe outlet end and having a surface area, and outlet channels sealed ator near the inlet end and having a surface area, the inlet channels andthe outlet channels defining filtration area;

wherein one or more of the porous wall surfaces defining the inletchannels comprise a base wall portion and filtration material depositsdisposed on the base wall portion to provide a composite microstructuresuch that at least a portion of the porous wall surfaces defining theinlet channels are comprised of the filtration material deposits forminga porous inorganic layer having a porosity greater than 90% and thecomposite microstructure having a porosity (ε) as measured by mercuryporosimetry, a median pore diameter (D₅₀) as measured by mercuryporosimetry, a permeability factor (κ) and an Effective MicrostructuralFactor (EMF) measured wherein,

the composite microstructure is characterized by a NormalizedMicrostructure Filtration Value NMFV=EMF/(ε^(0.43)/D₅₀^(5/3))_(base wall properties) of 2 or larger and a NormalizedPermeability Value NPV=κ_(effective)/(εD₅₀²/66.7)_(base wall properties) of 0.2 or larger.

120. The particulate filter of embodiment 119, wherein one or more ofthe porous wall surfaces defining the inlet channels comprise a basewall portion comprised of a first ceramic composition and filtrationmaterial deposits disposed on the base wall portion are comprised of asecond ceramic composition, and the first and second ceramiccompositions differ.

121. The particulate filter of embodiment 119, wherein the porousinorganic layer has average thickness of greater than or equal to 0.5 μmand less than or equal to 30 μm.

122. The particulate filter of embodiment 119, wherein the secondceramic composition is comprised of alumina or silica, or a combinationthereof.

123. The particulate filter of embodiment 119 wherein the second ceramiccomposition is selected from the group consisting of CaO, Ca(OH)₂,CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃, Al(OH)₃, calcium aluminates,magnesium aluminates, and mixtures thereof.

124. The particulate filter of embodiment 119, wherein the first ceramiccomposition is cordierite and the second ceramic composition is alumina.

125. The particulate filter of embodiment 119, wherein the porousinorganic layer comprises an oxide ceramic or an aluminum silicate.

126. The particulate filter of embodiment 119, wherein the porousinorganic layer covers at least 70% of the porous wall surfaces.

127. The particulate filter of embodiment 119, wherein the porousinorganic layer covers at least 90% of the porous wall surfaces.

128. The particulate filter of embodiment 119, wherein the inlet end andthe outlet end are spaced apart by an axial length, and the porousinorganic layer extends at least 60% along the axial length.

129. The particulate filter of embodiment 119, wherein the porousinorganic layer extends at least 60% of a distance between the inlet endand the outlet end.

130. The particulate filter of embodiment 122, wherein greater than 90%of the porous inorganic layer is disposed on the porous wall surfaces asa continuous coating.

131. The particulate filter of embodiment 119, wherein the porousceramic honeycomb structure has a porosity from greater than or equal to50% to less than or equal to 70%.

132. The particulate filter of embodiment 119, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 10 μm.

133. The particulate filter of embodiment 119, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 15 μm.

134. The particulate filter of embodiment 119, wherein the porousceramic honeycomb structure has a bulk median pore size from greaterthan or equal to 8 μm to less than or equal to 25 μm.

135. The particulate filter of embodiment 119, wherein the particulatefilter exhibits a change in filtration efficiency of less than 5% afterbeing exposed to to a high flow condition of 850 Nm³/h of air for oneminute at room temperature, and wherein the change in filtrationefficiency is determined by measuring a difference between a number ofsoot particles that are introduced into the particulate filter and anumber of soot particles that exit the particulate filter before andafter exposure to the high flow condition, wherein the soot particleshave a median particle size of 300 nm, a soot particle concentration of500,000 particles/cm³ in a stream of air flowed through the particulatefilter at room temperature and at a velocity of 1.7 m/s as measured by aparticle counter.

136. The particulate filter of embodiment 119, wherein the filtrationmaterial deposits comprise synthetic mullite.

137. The ceramic filter of embodiment 119, wherein the filtrationmaterial deposits are sintered to the porous ceramic base wall portion.

138. A particulate filter comprising:

a honeycomb body comprising a plugged porous ceramic honeycomb structurecomprising a plurality of intersecting porous walls comprising porouswall surfaces that define a plurality of channels extending from aninlet end to an outlet end of the structure, the plurality of channelscomprising inlet channels sealed at or near the outlet end and having asurface area, and outlet channels sealed at or near the inlet end andhaving a surface area, the inlet channels and the outlet channelsdefining filtration area;

wherein one or more of the porous wall surfaces defining the inletchannels comprise a base wall portion and filtration material depositsdisposed on the base wall portion,

wherein the filtration material deposits are disposed on the base wallportions to provide a porous inorganic layer having a porosity greaterthan 90%,

and wherein the particulate filter exhibits a change in filtrationefficiency of less than 5% after being exposed to to a high flowcondition of 850 Nm³/h of air for one minute at room temperature, andwherein the change in filtration efficiency is determined by measuring adifference between a number of soot particles that are introduced intothe particulate filter and a number of soot particles that exit theparticulate filter before and after exposure to the high flow condition,wherein the soot particles have a median particle size of 300 nm a sootparticle concentration of 500,000 particles/cm³ in a stream of airflowed through the particulate filter at room temperature and at avelocity of 1.7 m/s as measured by a particle counter.

139. The particulate filter of embodiment 138, wherein one or more ofthe porous wall surfaces defining the inlet channels comprise a basewall portion comprised of a first ceramic composition and filtrationmaterial deposits disposed on the base wall portion are comprised of asecond ceramic composition, and the first and second ceramiccompositions differ.

140. The particulate filter of embodiment 138, wherein the porousinorganic layer has average thickness of greater than or equal to 0.5 μmand less than or equal to 30 μm.

141. The particulate filter of embodiment 138, wherein the secondceramic composition is comprised of alumina or silica, or a combinationthereof.

142. The particulate filter of embodiment 138, wherein the secondceramic composition is selected from the group consisting of CaO,Ca(OH)₂, CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃, Al(OH)₃, calciumaluminates, magnesium aluminates, and mixtures thereof.

143. The particulate filter of embodiment 138, wherein the first ceramiccomposition is cordierite and the second ceramic composition is alumina.

144. The particulate filter of embodiment 138, wherein the porousinorganic layer comprises an oxide ceramic or an aluminum silicate.

145. The particulate filter of embodiment 138, wherein the porousinorganic layer covers at least 70% of the porous wall surfaces.

146. The particulate filter of embodiment 138, wherein the porousinorganic layer covers at least 90% of the porous wall surfaces.

147. The particulate filter of embodiment 119, wherein the inlet end andthe outlet end are spaced apart by an axial length, and the porousinorganic layer extends at least 60% along the axial length.

148. The particulate filter of embodiment 138, wherein the porousinorganic layer extends at least 60% of a distance between the inlet endand the outlet end.

149. The particulate filter of embodiment 122, wherein greater than 90%of the porous inorganic layer is disposed on the porous wall surfaces asa continuous coating.

150. The particulate filter of embodiment 138, wherein the porousceramic honeycomb structure has a porosity from greater than or equal to50% to less than or equal to 70%.

151. The particulate filter of embodiment 138, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 10 μm.

152. The particulate filter of embodiment 138, wherein the porousceramic honeycomb structure has a bulk median pore size greater than orequal to 15 μm.

153. The particulate filter of embodiment 138, wherein the porousceramic honeycomb structure has a bulk median pore size from greaterthan or equal to 8 μm to less than or equal to 25 μm.

154. The particulate filter of embodiment 138, wherein the particulatefilter exhibits a change in filtration efficiency of less than 5% afterbeing exposed to to a high flow condition of 850 Nm³/h of air for oneminute at room temperature, and wherein the change in filtrationefficiency is determined by measuring a difference between a number ofsoot particles that are introduced into the particulate filter and anumber of soot particles that exit the particulate filter before andafter exposure to the high flow condition, wherein the soot particleshave a median particle size of 300 nm a soot particle concentration of500,000 particles/cm³ in a stream of air flowed through the particulatefilter at room temperature and at a velocity of 1.7 m/s as measured by aparticle counter.

155. The particulate filter of embodiment 138, wherein the filtrationmaterial deposits comprise synthetic mullite.

156. The ceramic filter of embodiment 119, wherein the filtrationmaterial deposits are sintered to the porous wall surface.

157. A method of making a honeycomb body, the method comprising:

-   -   contacting an inorganic layer precursor with a gaseous carrier        fluid;    -   depositing the inorganic layer precursor on a porous ceramic        honeycomb structure by flowing the gaseous carrier fluid to the        porous ceramic honeycomb structure, the porous ceramic honeycomb        structure comprising a plurality of intersecting porous walls        arranged in a matrix of cells, the porous walls comprising        porous wall surfaces that define a plurality of channels        extending from an inlet end to an outlet end of the structure,        the plurality of channels comprising inlet channels sealed at or        near the outlet end and having a surface area, and outlet        channels sealed at or near the inlet end and having a surface        area; and    -   binding the inorganic layer precursor to the porous ceramic        honeycomb structure to form a porous inorganic layer, wherein    -   the porous inorganic layer has a porosity of greater than 90%,        and    -   the porous inorganic layer has an average thickness of greater        than or equal to 0.5 μm to less than or equal to 30 μm.

158. The method of making the honeycomb body of embodiment 157, whereinthe average thickness of the porous inorganic layer is greater than orequal to 1 μm to less than or equal to 20 μm.

159. The method of making the honeycomb body of embodiment 157, whereinthe average thickness of the porous inorganic layer is greater than orequal to 1 μm to less than or equal to 10 μm.

160. The method of making the honeycomb body of any of embodiments157-159, wherein the inorganic layer precursor comprises a ceramicprecursor material.

161. The method of making the honeycomb body of embodiment 160, whereinthe inorganic layer precursor comprises a solvent.

162. The method of making the honeycomb body of embodiment 161, whereinthe solvent is selected from the group consisting of methoxyethanol,ethanol, water, xylene. methanol, ethylacetate, benzene, and mixturesthereof.

163. The method of making the honeycomb body of embodiment 160, furthercomprising decomposing the inorganic layer precursor by contacting theinorganic layer precursor with a flame.

164. The method of making the honeycomb body of any of embodiments157-163, wherein the binding of the inorganic layer precursor to theceramic honeycomb body comprises sintering the inorganic layerprecursor.

165. The method of making the honeycomb body of embodiment 164, whereinthe sintering of the inorganic layer precursor is conducted at atemperature from greater than or equal to 450° C. to less than or equalto 1150° C. for a duration of greater than or equal to 20 minutes toless than or equal to 12 hours.

166. The method of making the honeycomb body of embodiment 165, whereinthe inorganic layer precursor is deposited on the ceramic honeycomb bodyas an amorphous phase having a porosity of greater than or equal to 98%,and

-   -   after sintering the inorganic layer precursor, an inorganic        layer having a crystalline phase and a porosity of greater than        or equal to 95% is present on the ceramic honeycomb body.

167. The method of making the honeycomb body of any of embodiments157-163, wherein the binding the inorganic layer precursor to theceramic honeycomb body comprises applying moisture to the ceramic layerprecursor.

168. The method of making the honeycomb body of any of embodiments157-163, wherein the ceramic layer precursor comprises a member selectedfrom the group consisting of tetraethyl orthosilicate, magnesiumethoxide and aluminum(III) tri-sec-butoxide, trimethylaluminum, AlCl₃,SiCl₄, Al(NO₃)₃, aluminum isopropoxide, octamethyl cyclotetrasiloxane,and mixtures thereof.

169. A method of making a honeycomb body, the method comprising:

-   -   contacting an inorganic layer precursor with a gaseous carrier        fluid;    -   vaporizing the inorganic layer precursor to form a gaseous        inorganic layer precursor;    -   exposing the gaseous inorganic layer precursor to a flame to        generate layer precursor particles;    -   depositing the layer precursor particles on a ceramic honeycomb        structure by flowing the gaseous carrier fluid to the ceramic        honeycomb structure; and    -   sintering the inorganic layer precursor particles to the ceramic        honeycomb body to form a porous inorganic layer, wherein    -   the porous inorganic layer has a porosity of greater than 90%,        and    -   the porous inorganic layer has an average thickness of greater        than or equal to 0.5 μm to less than or equal to 30 μm.

170. The method of making the honeycomb body of embodiment 169, whereinthe porous inorganic layer comprises an oxide ceramic or an aluminumsilicate.

171. The method of making the honeycomb body of embodiment 170, whereinthe oxide ceramic comprises synthetic mullite.

EXAMPLES

Embodiments will be further clarified by the following examples.

Example 1

Flame pyrolysis with liquid precursor. This example tests the chemicaldurability and physical stability of a ceramic layer deposited on acordierite honeycomb body. A layer precursor was formed from 2 partstetraethyl orthosilicate and three parts aluminum (III) tri-sec-butoxidein a methoxyethanol/ethanol (1:1 volume ratio) solvent. The layerprecursor was fed at a flow rate of 1 mL/min and contacted with anoxygen vaporizing gas that was fed at a flow rate of 5 L/min, whichvaporized the layer precursor. The vaporized layer precursor wasdecomposed in a flame and thereafter deposited as an amorphous phaselayer. The properties of the cordierite honeycomb body are listed inTable 1 below:

TABLE 1 Dimension (Dia. × CPSI/Wall Pore Size Length) thickness (μm)Porosity Honeycomb 5.66″ × 4.5″ 200/8.5 14 55% Body 1

Subsequently, the decomposed layer precursor was sintered by heating to1150° C. for 30 min to form a crystalline phase ceramic layer on thecordierite honeycomb body (i.e., a honeycomb body). For testingpurposes, a soot generating device (CAST2) was used to generateparticles having an average particle diameter of 120 nm in the presenceof an air flow rate of 350 L/minute (21 Nm³/h). The filtrationefficiency of Comparative Example 1, which is a honeycomb body withoutan inorganic coating, and Example 1, which is a honeycomb body with aninorganic coating, are provided in Table 2 below.

TABLE 2 Filtration Efficiency (FE) Comparison Lab FE_(mass) at LabFE_(mass) at 0.01 Lab FE_(mass) at 0.1 Maximum lab Soot loading @ Ref 0g/l soot (%) g/l soot (%) g/l soot (%) FE_(mass) (%) FE_(max) (g/L)Comp. Ex. 1 73.4 88.3 100.0 100.0 8.7E−02 Example 1 94.7 98.5 100.0100.0 4.4E−02

As shown in Table 2, the filtration efficiency of Example 1 is muchhigher at low soot loads than the filtration efficiency of ComparativeExample 1. Thus, a DPF or GPF with an inorganic coating according toembodiments disclosed and described herein will not be required toundergo the time-extensive process of building up a soot layer beforethe filter is able to achieve a high filtration efficiency, such as, forexample, a filtration efficiency of greater than 90%. FIG. 6 is agraphical representation of the filtration efficiency versus sootloading, and shows the increased filtration efficiency provided byadding an inorganic layer to a honeycomb body according to embodimentsdisclosed and described herein.

FIGS. 7A and 7B graphically depict the backpressure of Example 1 andComparative Example 1. FIG. 7A is a graphical depiction of thebackpressure (kPa) versus flow rate (Nm³/h) for Example 1 andComparative Example 1. As is shown in FIG. 7A, the backpressure versusflow rate is very similar for both Example 1 and Comparative Example 1.Thus, as shown in FIG. 7A, there is not a significant backpressurepenalty versus flow rate when an inorganic layer according toembodiments disclosed and described herein is applied to a honeycombbody. FIG. 7B is a graphical depiction of the backpressure (kPa) versussoot load level (g/L) for Example 1 and Comparative Example 1. As shownin FIG. 7B, the backpressure at every measured soot load shows less of abackpressure for Example 1 than for Comparative Example 1. Thus, thereis not backpressure penalty for using an inorganic layer according toembodiments disclosed and described herein at various soot loads.

Table 3 below shows various properties of the inorganic layer of Example1, and FIGS. 8A and 8B are SEM photographs of the inorganic layer ofExample 1 taken at 5 μm and 1 μm magnification, respectively.

TABLE 3 Property Characterization Method Composition Energy DispersiveX-ray 3Al₂O₃ · 2SiO₂ Spectroscopy (EDX) Loading Weight measurement  0.34g/L Inorganic layer surface Brunauer, Emmett and Teller 105.7 m²/g areaas-deposited (BET) Inorganic layer surface BET  41.3 m²/g area aftersinter Permeability Modeled from pressure drop 3.00E−14 m² data Porosityas deposited Based on density calculation 97.8% of the inorganic layerPorosity after sinter Based on density calculation 96.5% of theinorganic layer

Example 2

Flame pyrolysis with vapor precursor. Aluminium isopropoxide andoctamethyl cyclotetrasiloxane were used as the precursors forxAl₂O₃·ySiO₂. The precursor was heated up and the produced vapor wascarried by N₂. The composition of the as-deposited layer was controlledin the window of 1.5≤x/y≤2. The vaporized layer precursor was decomposedin a flame and thereafter deposited as an amorphous phase decomposedlayer precursor on a cordierite honeycomb body having the propertieslisted in Table 4.

TABLE 4 Dimension (Dia. × CPSI/Wall Pore Size Length) thickness (μm)Porosity Honeycomb Body 2 4.055″ × 5.47″ 200/8.5 14 55%

In Table 4, CPSI is cells per square inch, porosity is measured bymercury intrusion porosimetry.

Subsequently, the decomposed layer precursor was sintered by heating to1150° C. for 30 min to form a crystalline phase ceramic layer on thecordierite honeycomb body (i.e., a honeycomb body). Soot generation wasconducted in accordance with Example 1. The filtration efficiency (FE)of Comparative Example 2, which is a honeycomb body without an inorganiccoating, and Example 2, which is a honeycomb body with an inorganiccoating are provided in Table 5 below.

TABLE 5 Lab FE_(mass) at Lab FE_(mass) at 0.01 g/l soot Lab FE_(mass) atMaximum lab Soot loading @ 0 g/l soot (%) (%) 0.1 g/1 soot (%) FE_(mass)(%) FE_(max) (g/L) Comp. Ex. 2 58.9 73.5 99.3 100.0 1.4E−01 Example 291.2 97.9 100.0 100.0 3.8E−02

As shown in Table 5, the filtration efficiency of Example 2 is muchhigher at low soot loads than the filtration efficiency of ComparativeExample 2. Thus, a DPF or GPF with an inorganic coating according toembodiments disclosed and described herein will not be required toundergo the time-extensive process of building up a soot layer beforethe filter is able to achieve a high filtration efficiency, such as, forexample, a filtration efficiency of greater than 90%. FIG. 9 is agraphical representation of the filtration efficiency versus sootloading, and shows the increased filtration efficiency provided byadding an inorganic layer to a honeycomb body according to embodimentsdisclosed and described herein.

FIGS. 10A and 10B graphically depict the backpressure of Example 2 andComparative Example 2. FIG. 10A is a graphical depiction of thebackpressure (kPa) versus flow rate (Nm³/h) for Example 2 andComparative Example 2. As is shown in FIG. 10A, the backpressure versusflow rate is very similar for both Example 2 and Comparative Example 2.Thus, as shown in FIG. 10A, there is not a significant backpressurepenalty versus flow rate when an inorganic layer according toembodiments disclosed and described herein is applied to a honeycombbody. FIG. 10B is a graphical depiction of the backpressure (kPa) versussoot load level (g/L) for Example 2 and Comparative Example 2. As shownin FIG. 10B, the backpressure at every measured soot load shows less ofa backpressure for Example 2 than for Comparative Example 2. Thus, thereis not backpressure penalty for using an inorganic layer according toembodiments disclosed and described herein at various soot loads.

Table 6 below shows various properties of the inorganic layer of Example2, and FIGS. 11A and 11B are SEM photographs of the inorganic layer ofExample 2 taken at 5 μm and 1 μm magnification, respectively.

TABLE 6 Property Characterization method Composition EDX 3Al₂O₃ · 2SiO₂~ 2Al₂O₃ · SiO₂ Loading Weight measurement 0.34 g/L Inorganic layersurface BET 56.3 m²/g area as-deposited Inorganic layer surface BET 47.6m²/g area after sinter Porosity as deposited Based on densitycalculation 98.0% of the inorganic layer Porosity after sinter Based ondensity calculation 97.4% of the inorganic layerFIG. 12 shows an XRD scan of the as-deposited inorganic layer(decomposed layer precursor), which depicts an amorphous phase; and ofthe inorganic layer after sintering, which depicts a crystalline phaseceramic layer having peaks that are consistent with the mullite standardpattern.

Example 3

Flame pyrolysis with vapor precursors. This example tests the chemicaldurability and physical stability of a ceramic layer deposited on acordierite honeycomb body. FIG. 19 is a flow chart of the flamepyrolysis process used in this example. Ceramic precursors of syntheticmullite were: aluminium chloride (AlCl₃) in solid form, and silicontetrachloride (SiCl₄) in liquid form. Nitrogen (N₂) was used as acarrier gas for AlCl₃ at 2.0 L/minute and for SiCl₄ at 0.3 L/minute. Thesolid AlCl₃ and its carrier gas passed through a heated sublimator (165°C.) to form gaseous AlCl₃. The liquid SiCl₄ and its carrier gas passedthrough a heated bubbler (35° C.) to form gaseous SiCl₄. The targetedAl/Si mass ratio was in the range of 2.9 to 3.8. All of the heatedvessels and pipes were monitored by T-type thermocouples and insulated.T-type thermocouples are accurate with high sensitivity withintemperature range −270 to 400° C. All the gas flow was managed by thecalibrated mass flow controllers (MFCs) for flow precision. Processcontrol of Al/Si mass ratio in the range of 2.9 to 3.8 A was achievedalong with a stable yield of mullite composition during a long termoperation (14-21.5 hours).

A layer precursor comprising the gaseous AlCl₃ and SiCl₄, which wereentrained in heated nitrogen, was transported into a burner. The burnerhad four functional gas lines inside. A methane/oxygen premixed flamewith an optimal ratio of 1.25 provided a reaction zone for combustion ofthe layer precursor. An inner-shield O₂ gas (190° C. and 2.0 L/minute)was used to lift the combustion area and force as-formed particles awayfrom the flame to keep the reaction zone clean. Supplementary O₂ gas(1.5 L/minute) provided excess oxygen to complete combustion reactionsand assisted to stabilize the flame. As needed, additional O₂ gas (up to8 L/minute) may be supplied. A central tube allowed the layer precursorto pass through and get into the flame to generate particles. Fourdifferent channels could cooperate with each other to control the flamewith great flexibility. Typically, all components of the ceramicprecursor vaporization equipment (e.g., vessels and pipes) and of theburner were insulated and preheated to above 120° C.-190° C. to avoidvapor condensation and channel block. Through control of heatingtemperature and carrier gas flow rate, the composition of the finalproduct was controlled. The burner may operate in a range of about 175°C. to 190° C. to assist with avoiding condensation in the central tubeand/or seal damage due to overheating.

In the burner, the layer precursor was exposed to a flame formed by amixture of methane (CH₄) (5.0 L/minute) and oxygen (O₂) (4.0 L/minute),which provided a high temperature reaction zone and moisture ambienceowing to the CH₄ combustion. Once the layer precursor contacted with H₂Oin the flame, the chlorides hydrolyzed and oxides particles formed toresult in a decomposed layer precursor. The intense collision betweenthe primary particles resulted in coagulation and coalescence under thehigh temperature. A portion of them grew into big particles, a largenumber of them were partially sintered together to form aggregates, andthe rest particles became agglomerates relying on physical bonds. Allthe particle and particle groups escaped from the flame within severalmilliseconds because of the steep temperature gradient and high gas flowvelocity of the flame. It is noted that the product morphology,especially the particle size, could be adjusted by the presence ofanother heated N₂ gas to further dilute the ceramic precursor vaporsbefore entering the flame.

As-formed particles of the decomposed layer precursor were deposited ona stainless steel mesh (316 L, 2000 DPSI) and a ceramic coupon (cut offfrom a GPF honeycomb) placed on a cylinder mounted above the flame. Forfiltration efficiency and pressure drop analysis, as-formed particleswere deposited on full-size ceramic honeycombs ((GC 4.055″-200/8) in awind tunnel, which was employed to enhance the deposition uniformity andcollection efficiency. All the deposition processes were aided by use ofa vacuum pump.

Once the particles of the decomposed layer precursor were deposited ontoa structure (e.g., stainless steel mesh, ceramic coupon, or full-sizeceramic honeycomb) was completed, the structure was sintered in an ovenset at 1150° C. for 30 minutes. Upon sintering, a crystalline phaseceramic layer was formed.

FIGS. 13A and 13B are scanning electron microscope images at differingmagnifications of an amorphous phase decomposed layer precursordeposited on a honeycomb body. The as-deposited decomposed layerprecursor was porous and all of the particles packed loosely to form acontinuous structure. FIGS. 13C and 13D are scanning electron microscopeimages at differing magnifications of a crystalline phase ceramic layerformed after sintering of the amorphous phase decomposed layerprecursor. Thermal treatment changed the layer morphology which evolvedinto a well-connected structure while the particle grew from about 20-40nm (FIGS. 13A-B) to about 60-80 nm (FIGS. 13C-D).

FIG. 14 shows an XRD scan of the decomposed layer precursor:as-deposited, after exposure to 850° C. for 6 hours, after exposure to850° C. for 12 hours, and after sintering at 1150° C. for 0.5 hours. Theas-deposited layer was amorphous while the main peaks of the 1150° C.sintered layer corresponded to a mullite standard pattern. As-depositedparticles could not crystallize at low temperature, such as 850° C.,even for up to 12 hours. The vapor precursor based particles behavedsimilarly with that using liquid precursor in crystallization even therewas distinct difference in their initial particle size.

BET techniques were conducted to investigate particle size. The resultsare shown in Table 7.

TABLE 7 As- 850° C., 850° C., 850° C., 1150° C., deposited 3 h 6 h 12 h0.5 h BET surface 61.1 62.8 60.3 62.2 47.6 area (m²/g) Equivalent 35.134.1 35.5 34.5 45.0 Diameter (nm)

In Table 7, surface area of the as-deposited particles was 61.1 m²/g,which decreased to 47.6 m²/g after sintering at 1150° C. Particle sizechanged slightly when sintered at 850° C. The results were consistentwith the XRD scans. The sintering process was effective in introducing acrystallized phase, improving structure integrity without significantlysacrifice on the porosity of the mullite layer. The results aboveindicate that vapor precursor process could achieve the same results asliquid precursor in mullite preparation including composition, sinteredparticle size and even the sintered inorganic layer morphology.

Filtration efficiency of a gasoline particulate filter (GPF) wasanalyzed by depositing the synthetic mullite of this example on a fullsize GPF (GC 4.055″-200/8). Simulated engine particulate filtration test(for 120 nm particle size, flow rate of 21 Nm³/h) was used to evaluatethe filtration efficiency while the clean backpressure test was used todetermine pressure drop penalty.

FIG. 15 is a graphical representation of the filtration efficiency (FE)versus soot loading, and shows the increased filtration efficiencyprovided by adding an inorganic layer to a honeycomb body according toembodiments disclosed and described herein. In FIG. 15, ComparativeExample 3 is a honeycomb body without an inorganic layer and Example 3has the mullite layer of this example. Initial FE increased for Example3. Comparative Example 3 for a soot loading of 0.01g/L reached an FE of97.4%. In contrast, Example 3, as much less soot accumulation couldreach 100% FE.

Table 8 is a sample evaluation of Example 3.

TABLE 8 Example 3 Filtration efficiency (FE) 97.4% Particulate Number5.9 × 10¹⁰ #/Km (PN) Clean dP +5.7% Soot Loaded dP −5.4% @ 2 g/L Thermalrobustness Pass Thermal shock: >850° C. Pass Operating window: 1150° C.Pass Hydrothermal: 1150° C., 10 wt % moisture Mechanical integrity PassVibration (76 g, 200 Hz, 2 h) Pass High flow (850 Nm³/h cold flow)

In accordance with Table 8, an inorganic layer of mullite provides ahigh filtration efficiency (greater than 97%) with a low pressure droppenalty (only about 5.7%). The particle number passed through the layerwas 5*10¹⁰ #/Km and the soot loaded dP@2 g/L was −5.4%. Besidesperformance, strength and durability of the inorganic layer is relevantto application in a gasoline particulate filter (GPF). Layer thermalrobustness was demonstrated by thermal shock, operating window andhydrothermal test while mechanical integrity test included vibration andhigh flow in Table 8. Therefore, existing properties of the startinghoneycomb body remained unchanged (or the change was negligible) withaddition of the layer. Following thermal and mechanical reliabilitytesting, there was little to no degradation in filtration efficiency(FE) for the composite honeycomb and inorganic layer.

FIGS. 16A and 16B graphically depict the backpressure of Example 3 andComparative Example 3. FIG. 16A is a graphical depiction of thebackpressure (kPa) versus flow rate (Nm³/h) for Example 3 andComparative Example 3. For Example 3, the initial FE of membrane samplewas up to 90.1% (FIG. 15), and the DP penalty was only 5.7% inaccordance with FIG. 16A, which was much lower than a traditionaldip-coating filter. In FIG. 16B, backpressure rose up with the sootloading amount increasing. Example 3 exhibited a lower pressure droppenalty than Comparative Example 3 when the soot loading was higher than0.5 g/L. This could be explained that the layer provided the filter withan “on-wall” coating mode instead of “in-wall”, which occurs in commonparts.

The particulate filter made according to Example 3 was tested for achange in filtration efficiency as follows. The particulate filter ofExample 3 exposed to a high flow condition of 850 Nm³/h of air for oneminute at room temperature. A change in filtration efficiency wasdetermined by measuring the difference between a number of sootparticles that are introduced into the particulate filter and a numberof soot particles that exit the particulate filter before and afterexposure to the high flow condition. The soot particles were particlesfrom cigarette smoke having a median particle size of 300 nm in a streamof air with a soot particle concentration of 500,000 particles/cm³ thatwas flowed through the particulate filter of Example 3 at a flow rate of51 Nm³/h, room temperature, and a velocity of 1.7 m/s for one minute.Filtration efficiency was determined by measuring particle count usingan 0.1 CFM Lighthouse Handheld 3016 particle counter available fromLighthouse Worldwide Solutions. The measurement was performed on theparticulate filter of Example 3 as manufactured, and then after exposureto the high flow condition of 850 Nm³/h of air for one minute at roomtemperature. The particulate filter of Example 3 exhibited a change infiltration efficiency of less than 1% after exposure to the high flowcondition of 850 Nm³/h of air for one minute at room temperature. Thisresult indicates that the filtration material deposits exhibitedexcellent durability in that the filtration material deposits remainedin place and continued to be effective in providing enhanced filtrationefficiency for the particulate filter.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus, it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A particulate filter comprising: a honeycomb bodycomprising a plugged porous ceramic honeycomb structure comprising aplurality of intersecting porous walls comprising porous wall surfacesthat define a plurality of channels extending from an inlet end to anoutlet end of the porous ceramic honeycomb structure, the plurality ofchannels comprising inlet channels sealed at or near the outlet end andhaving a surface area, and outlet channels sealed at or near the inletend and having a surface area, the inlet channels and the outletchannels defining filtration area; wherein one or more of the porouswall surfaces defining the inlet channels comprise a base wall portionand filtration material deposits disposed on and bound to the base wallportion by thermal sintering or fusing to provide a compositemicrostructure and the composite microstructure having a porosity (ε) asmeasured by mercury porosimetry, a median pore diameter (D₅₀) asmeasured by mercury porosimetry, a permeability factor (κ) and anEffective Microstructural Factor (EMF) measured, wherein the compositemicrostructure is characterized by a Normalized MicrostructureFiltration Value NMFV=EMF/(ε^(0.43)/D₅₀ ^(5/3))_(base wall properties)of 2 or larger and a Normalized Permeability ValueNPV=κ_(effective)/(εD₅₀ ²/66.7)_(base wall properties) of 0.2 or larger,wherein the particulate filter exhibits a change in filtrationefficiency of less than 5% after being exposed to a high flow conditionof 850 Nm³/h of air for one minute at room temperature, and wherein thechange in filtration efficiency is determined by measuring a differencebetween a number of soot particles that are introduced into theparticulate filter and a number of soot particles that exit theparticulate filter before and after exposure to the high flow condition,wherein the soot particles have a median particle size of 300 nm a sootparticle concentration of 500,000 particles/cm³ in a stream of airflowed through the particulate filter at room temperature and at avelocity of 1.7 m/s as measured by a particle counter.
 2. Theparticulate filter of claim 1, wherein one or more of the porous wallsurfaces defining the inlet channels comprise a base wall portioncomprised of a first ceramic composition and filtration materialdeposits disposed on the base wall portion are comprised of a secondceramic composition, and the first and second ceramic compositionsdiffer.
 3. The particulate filter of claim 1, wherein the filtrationmaterial deposits have an average thickness of greater than or equal to0.5 μm and less than or equal to 30 μm.
 4. The particulate filter ofclaim 1, wherein the second ceramic composition is comprised of aluminaor silica, or a combination thereof.
 5. The particulate filter of claim1 wherein the second ceramic composition is selected from the groupconsisting of CaO, Ca(OH)₂, CaCO₃, MgO, Mg(OH)₂, MgCO₃, SiO₂. Al₂O₃,Al(OH)₃, calcium aluminates, magnesium aluminates, and mixtures thereof.6. The particulate filter of claim 1, wherein the first ceramiccomposition is cordierite and the second ceramic composition is alumina.7. The particulate filter of claim 1, wherein the filtration materialdeposits comprise an oxide ceramic or an aluminum silicate.
 8. Theparticulate filter of claim 1, wherein the filtration material depositscover at least 70% of the porous wall surfaces.
 9. The particulatefilter of claim 1, wherein the filtration material deposits cover atleast 90% of the porous wall surfaces.
 10. The particulate filter ofclaim 1, wherein the inlet end and the outlet end are spaced apart by anaxial length, and the filtration material deposits extend at least 60%along the axial length.
 11. The particulate filter of claim 1, whereinthe filtration material deposits extend at least 60% of a distancebetween the inlet end and the outlet end.
 12. The particulate filter ofclaim 1, wherein greater than 90% of the filtration material depositsare disposed on the porous wall surfaces as a continuous coating. 13.The particulate filter of claim 1, wherein the porous ceramic honeycombstructure has a porosity from greater than or equal to 50% to less thanor equal to 70%.
 14. The particulate filter of claim 1, wherein theporous ceramic honeycomb structure has a bulk median pore size greaterthan or equal to 10 μm.
 15. The particulate filter of claim 1, whereinthe porous ceramic honeycomb structure has a bulk median pore sizegreater than or equal to 15 μm.
 16. The particulate filter of claim 1,wherein the porous ceramic honeycomb structure has a bulk median poresize from greater than or equal to 8 μm to less than or equal to 25 μm.17. The particulate filter of claim 1, wherein the particulate filterexhibits a change in filtration efficiency of less than 5% after beingexposed to to a high flow condition of 850 Nm³/h of air for one minuteat room temperature, and wherein the change in filtration efficiency isdetermined by measuring a difference between a number of soot particlesthat are introduced into the particulate filter and a number of sootparticles that exit the particulate filter before and after exposure tothe high flow condition, wherein the soot particles have a medianparticle size of 300 nm, a soot particle concentration of 500,000particles/cm³ in a stream of air flowed through the particulate filterat room temperature and at a velocity of 1.7 m/s as measured by aparticle counter.
 18. The particulate filter of claim 1, wherein thefiltration material deposits comprise synthetic mullite.
 19. Theparticulate filter of claim 1, wherein the filtration material depositshave a porosity greater than 90%.